«li 







FHTRT 



INSTRUCTION* 

i^^^Y^T^^»^^^y»tv^v<^^ v ^'^^Y»tVH^>l^Vl'^'Ylt 




rare J /T/Sf 

Book. H'jqZ 

Copyright^ UOLLh 

CQFXRIGHT DEPOSE 



MODERN 

Electrical Construction 

A RELIABLE, PRACTICAL GUIDE FOR THE 
BEGINNER IN ELECTRICAL CONSTRUCTION 
SHOWING THE LATEST APPRC '3D METHODS 
OF INSTALLING WORK OF ALL KINDS AC- 
CORDING TO THE SAFETY RULES OF THE 

National Board of Fire Underwriters 



By 

HENRY C. HORSTMANN 

and 

VICTOR H. TOUSLEY 

Authors of li Modern Wiring Diagrams and Descriptions" Elec- 
trical Wiring and Construction Tables , " lt Practical 
Armature and Magnet Winding," " Electricians 
Operating and Testing Manual " Etc, 



illustrate 



Fifth Edition — Revised and Enlarged 




CHICAGO 
FREDERICK J. DRAKE & CO., PUBLISHERS 



t Kis\ 






Copyright 


1904 


BY 




HORTSMANN & 


TOUSLEY 


Copyright 


1908 


BY 




HORTSMANN & 


TOUSLEY 


Copyright 


1911 


BY 




HORTSMANN & 


TOUSLEY 


Copyright 


1913 


BY 




HORTSMANN & 


TOUSLEY 


Copyright 


1916 


BY 




HORTSMANN & 


TOUSLEY 




OCT 13 1916 

©CI.A438860 



£ 



*o 



- r 



PREFACE 



In this volume an attempt is made to provide the beginner 
in electrical construction work with a reliable, practical guide ; 
one that is to tell him exactly how to install his work in ac- 
cordance with the latest approved methods. 

It is also intended to give such an elaboration of "safety 
rules ,, as shall make the book valuable to the finished work- 
man as well. To this end the rules of the "National Electrical 
Code" of the National Board of Fire Underwriters have been 
given in full, and used as a text in connection with which 
there is interspersed in the proper places a complete explana- 
tion of such work as the rules may apply to. This method of 
teaching and explaining practical electricity may at first glance 
seem somewhat haphazard, but it resembles very closely the 
actual method by which the most successful, practical work- 
men have learned the trade. It is thought that explanations 
pertaining directly to the work in hand will be more deeply 
considered and more likely to be fully comprehended than 
explanations necessarily more abstract. 

It should be noted that, while the rules published in the 
"National Electrical Code" are standard and work done in 



conformity with them will be first-class, several of the larger 
cities have ordinances governing electrical work which con- 
flict in some details with these rules. Workers in such cities 
should, therefore, provide themselves with copies of these 
ordinances (usually obtainable without charge), and compare 
them with the rules given in this work. It is necessary for 
the electrical worker at all times to keep himself posted, for 
safety rules are liable to change. 

The tables concerning screws, nails, number of wires that 
can be used in conduit, etc., are especially prepared for this 
volume, and give to it particular value for practical men. 

The Authors. 



PREFACE TO SECOND EDITION 



The favorable reception which the first edition of this 
work has received at the hands of electrical workers generally 
has induced the authors to prepare this, the Second Edition. 
Considerable new matter, notably a section on Theater Wir- 
ing, has been added. All the necessary alterations and addi- 
tions have been made in the text to conform to the latest 
issue of the National Code, together with the required explan- 
ations and illustrations. Other sections have been extended 
and the whole work has been carefully gone over and re- 
vised wherever the progress of the art has made it desir- 
able. 

The Authors. 



PREFACE TO THE THIRD EDITION 



In a work of this kind it is of prime importance that it be 
kept abreast of the times. Safety rules are liable to change, 
in fact must do so to adapt themselves to the steadily increas- 
ing number of new inventions and devices brought upon the 
market. 

This work having found sufficient favor in the eyes of many 
instructors to warrant its adoption as a text-book, is to be 
revised and new matter added as often as notable changes in 
methods of construction or safety rules make it appear de- 
sirable. 

The latest additions and modifications of the "National 
Electrical Code" are contained in an appendix which should 
be consulted. New illustrations are inserted in the body of 
the work as needed. 

The Authors. 



PREFACE TO FOURTH EDITION 



The favor with which former editions of this work have 
been received and the general reliance placed upon it by elec- 
trical workers everywhere has made it practically mandatory 
that it be kept strictly up-to-date. Since the National Elec- 
trical Code is subject to bi-ennial revision a similar revision of 
this work is advisable and it is the purpose hereafter to provide 
such. This work consists really of two parts, one being a 
literal transcription of the National Electrical Code, and the 
other consisting of comments and practical hints by the au- 
thors with the object of instructing wiremen in the installa- 
tion of electrical apparatus. 

While long experience has given the authors a peculiar fit- 
ness to speak upon the matters considered, it is, nevertheless, 
thought advisable to warn the reader that on all points that 
may not seem perfectly clear and harmonious it is best to 
consult the inspection department having jurisdiction; in other 
words, the authors wish distinctly to waive all claims to speak- 
ing officially on any part of the Code. 

It has been the aim of the authors to treat every branch of 
electrical construction work which may come under the super- 
vision of a practical wireman and for this reason a chapter 
on electric sign hanging and some notes on moving picture 
booths and installations have been added. 

This work deals only with construction. Should any wire- 
man be called upon to advise in the layout of lighting installa- 
tions much information of a useful and practical nature will 
be found in a recent work entitled "Modern Illumination, 
Theory and Practice" which may be considered as supple- 
mentary to this work. The Authors. 



CHAPTER I. 
The Electric Current. 

It is quite customary and convenient to speak of that 
agency by which electrical phenomena, such as heat, light, 
magnetism, and chemical action are produced as the electric 
current. In many ways this current is quite analogous to cur- 
rents of air or water. Just as water tends to flow from a 
higher to a lower level, and air from a region of greater 
density or pressure to one of lesser density, so do currents of 
electricity flow from a region of high pressure to one of low 
pressure. Currents of electricity form no exception whatever 
to the general law of all action, which is along the lines of 
least resistance. It must not be understood, however, that 
electricity actually flows in or along a conductor, as water 
does in a pipe, and the analogy must not be carried too far, for 
the flow of water in pipes is influenced by many conditions 
which do not influence a flow of electricity at all, and vice 
versa; there are conditions surrounding conductors, which 
influence the flow of electricity which do not affect the flow 
of water. 

Above all, let it be understood that electricity is not inde- 
pendent energy, any more than the belt which gives motion 
to a pulley is. In other words, it is not a prime mover, it is 
simply a medium which may be used for the transmission of 
energy, just as the belt is used. To use electricity as a 
medium for the transmission of energy, it must be, we may 
say, compressed, or, to use a more properly technical expres- 
sion, a difference of potential or pressure must be created in 
a system of conductors. This is very similar to the use of air 



8 



MODERN ELECTRICAL CONSTRUCTION. 



for power transmission; this must also be compressed so that 
a difference of pressure exists within a system of piping. 

It is the flow of electricity or air which takes place when 
switches or valves are operated and which tends to equalize 
this pressure, i. e., flow from high to low pressure, that does 
our work. The real energy, however, (so far as we are con- 
cerned), to which we must look for our initial motion in 
either case is derived from the coal which generates steam; 
or, in the case of water-driven machinery, the rays of the sun 
which evaporate water, allowing it to be carried to higher 
levels, from whence it flows downward over dams and falls 
on its way back to the lowest level. In the battery, the real 
energy is that of chemical action, which is transformed into 
electrical energy. 

The flow of current can take place only in a system of 
conductors which usually, for convenience, are made in the 
form of wires. The current for practical purposes may be 
considered as flowing along such wires only. It is not, how- 




Figure 1 

ever, necessary that these wires should be of any particular 
size, or consist all of the same material. In an electric bat- 
tery, part of the circuit consists of the liquid contained within 
the battery; the rest being made up usually of wire. In an 
incandescent light circuit part of the circuit consists of the 



ELECTRIC CURRENT. 9 

lamp filament (usually carbon), while the balance of the cir- 
cuit consists of copper wire. 

The flow of current is also said to have a certain direction ; 
that is, it is noticed that many of its effects are reversed when 
the terminals of the battery are reversed. Referring to Fig. 
1, which shows a battery of three cells, the current flows from 
the copper element at bottom of jar 1, along the wire to the 
zinc element at top of jar 2, thence through the liquid to the 
copper element at bottom of jar 2, and from there to the zinc 
at top of jar 3, etc., and finally through the wire a back to 
the starting point. Within the battery the current flows from 
the zinc to the copper and the decomposition of the zinc gen- 
erates the current. In the wire outside of the battery the cur- 
rent flows from the copper to the zinc as indicated by arrows. 
The combination of battery and wire is known as an electric 
circuit. The current will flow in this circuit only while it 
is complete, that is while each wire connects to its proper 
place as shown. If any wire is disconnected, the current flow 
will cease. Such a circuit is said to be open, but when all 
connections are properly made it is said to be closed. 

Work can be obtained from a flow of current in many 
ways. If the current be forced to flow over a wire which is 
very small in proportion to the current carried, it will be 
heated thereby and finally melted if the current is excessive. 
This is how electric light is obtained. 

If a wire carrying current be wound many times about 
an iron bar this bar becomes a magnet; that is, while the cur- 
rent is flowing around it, the bar has the power to attract 
other objects of iron or steel. The bar if made of well an- 
nealed iron will be a magnet while current is flowing around 
it, but will cease to be magnetic whenever the current flow 
ceases. Upon this fact the operation of electric bells, telegraph 
instruments and motors is based. 

If a current of electricity flow through a properly arranged 



10 MODERN ELECTRICAL CONSTRUCTION. 

''bath," one of the plates will be gradually consumed and the 
other increased in weight. This effect is made use of in 
electro-plating, etc. If the jar contains water slightly acid- 
ulated and the current flows through it, the water will be 
decomposed and oxygen and hydrogen gas will be formed. 
This and many kindred effects are daily used in thousands of 
chemical laboratories. 

If a wire carrying an electric current be placed very close 
to another wire forming a closed circuit, a wave of current 
will be induced in that wire every time the current in the 
other is made or broken, i. e., whenever it starts to flow or 
stops flowing. This fact forms the basis of the alternating 
current transformer. 

All of these facts are used sometimes together, sometimes 
singly in measuring the electric current. 

Conductors and Insulators. 

Electrically speaking, all substances are divided into two 
classes. They are either conductors or insulators. By thi« 
is not meant that some substances can carry no current at 
all, for, as a matter of fact, there is no such thing as either a 
perfect conductor or a pecfect insulator. A current of elec- 
tricity can be forced through any substance, provided the pres- 
sure (E. M. F.) be made great enough, and there is no easier 
path open to the current. The two terms, conductor and 
insulator, are relative terms and must be understood simply 
to mean that the electrical resistance of a good conductor is 
infinitesimally small as compared to that of a good insulator. 
The lower the specific resistance of any substance, the better 
its conducting qualities; the higher the specific resistance of 
any substance, the better will be its insulating qualities. 

At the left is given a list of good conductors, in the order 
of their conductivity, the figures representing the relative con- 



ELECTRO- MOTIVE-FORCE. 11 

ductivity of these metals. A list of insulators is given at the 
right; all of these are more or less affected by moisture, los- 
ing their insulating qualities when wet. 

Silver 100.0 Dry air. Fiber. 

Copper 94.0 Rubber. Wood. 

Gold 73.0 Paraffin. Shellac. 

Platinum 16.6 Slate. 

Iron 15.5 Marble. 

Tin 11.4 Glass. 

Lead 7.6 Porcelain. 

Bismuth 1.1 Mica. 



Pressure or Electro-Motive Force. 

Currents of electricity flow only in obedience to electrical 
pressure. This pressure is measured and expressed in volts, 
the unit of electrical pressure being the volt. If we speak 
of water or steam pressure, we speak of it in pounds, the 
pound being the unit of measurement. In speaking of elec- 
trical pressure we refer to it as of so many volts. There is no 
direct connection between the pound and the volt, but each 
in its place means about the same thing. 

The volt is defined as that difference of potential (pres- 
sure) that must be maintained to force a current of one 
ampere through a resistance of one ohm. 

If we have a resistance greater than one ohm and wish to 
send a current of one ampere through it, we can do so by 
increasing the pressure or voltage, as it is termed, accordingly. 
The current flowing in a circuit can also be reduced by reduc- 
ing the voltage. 

The ordinary incandescent lamps operate at about 110 
volts pressure, although some are built for 220 volts. An elec- 
tric bell requires about 2 l / 2 volts (a battery of 2 cells) for 
proper operation. 



12 MODERN ELECTRICAL CONSTRUCTION. 

Resistance. 

We have seen that a flow of current always takes place 
along or in a conductor. Every conductor, no matter how 
large or small it may be, offers some resistance to this flow 
of current just as the water pipe offers more or less resistance 
to the flow of water. This resistance may be measured and 
expressed in ohms; the unit of electrical resistance being the 
ohm. The ohm is defined as that resistance which requires a 
difference of potential of one volt to send a current of one 
ampere through it. If we should desire to send a greater cur- 
rent through any resistance, we can do so by increasing the 
pressure, just as we can increase the flow of water in a pipe 
by increasing the pressure or head of water in the tank that 
supplies it. If the pressure is fixed we can decrease the 
current by using a wire of greater resistance or increase it by 
using wires of lesser resistance. 

The ohm is the resistance of a column of mercury 106.2 
centimeters long (about 3^ feet) and one square millimetre 
(about .0015 sq. in.), in cross-section, at the temperature of 
melting ice. 

The resistance of a No. 14 copper wire about 380 feet long 
is equal to one ohm. 

The resistance of all conductors increases directly as the 



3 

Figure 2 

length and decreases as the cross-section increases. In Figure 
2 the resistance of the two bars of copper is exactly equal. 
Bar No. 1 having a cross-section of 4 square inches and being 
4 feet long, while bar No. 2 has a cross-section of only 1 
square inch and is only one foot long. If bar No. 1 were 



OHMS LAW. 13 

reduced to a cross-section of 1 square inch, it would become 
16 feet long and would have a resistance 16 times as great as 
that of bar No. 2. 

Current. 

The electric current is the result of electrical pressure 
(volts) acting through a resistance, and is measured in 
amperes, the ampere being the unit of current strength. The 
ampere is denned as that current which will flow through a 
resistance of one ohm when a difference of potential or pres- 
sure of one volt is maintained at its terminals. 

The ampere expresses only the rate of flow, not the quan- 
tity. Knowing the amperes if we would know the quantity, 
we must multiply by the time that the rate of flow continues. 
Ihe rate of flow is analogous to the speed of a train; unless 
we know how long the train is to maintain a certain speed, we 
have no idea how far it is going. 

Quantity in electricity is measured in coulombs. The 
coulomb is the quantity of current delivered by a flow of one 
ampere in one second. 

Ohm's Law. 

Ohm's law expresses the relation of the three principal 
electrical units to each other and forms the basis of all elec- 
trical calculations. 

This law states that in any electric circuit (with direct 
current) the current equals the electro-motive force divided by 
the resistance. The current, we have already seen, is the 
medium which does our work. Current flow, we see from this 
law, can be increased either by increasing the electro-motive 
force, or electric pressure, which causes the flow; or by 
decreasing the resistance which tends to prevent current flow. 
Expressed in symbols it is this : I=E/R ; where I stands for 



14 MODERN ELECTRICAL CONSTRUCTION. 

current, E, for electro-motive force, and R for resistance. If, 
as an example, we have an electro-motive force (which we 
shall henceforth designate by the customary abbreviation, E. 
M. F.) of 110 volts and a resistance of 220 ohms, the resulting 
current will be 110 divided by 220=^2 ampere, being approxi- 
mately the current used in a 16 cp. incandescent lamp at 110 
volts. Thus it will be seen that by a very simple calculation 
we can find the current flow in any conductor if we but know 
the E. M. F. and the resistance of that circuit. 

This formula can also be used to find the E. M. F., if we 
know the value of current and the resistance, since E divided 
by R=I; I times R must equal E. If the current and resist- 
ance are known, we need only to multiply them together to find 
the E. M. F.; IXR=E. Knowing the current and E. M. F., 
we can find the value of the resistance by dividing the E. M. 
F. by the current ; E/I=R. 

As a practical application of these formulas: If we wish 
to know how much current a certain E. M. F. can force 
through a certain resistance, we must divide the E. M. F. 
(volts) by the resistance (ohms.) If we wish to know what 
E. M. F. (volts) will be necessary to force a certain cur- 
rent (amperes) through a certain resistance, we need only 
multiply the current (amperes) to be obtained by the resist- 
ance in ohms. If we wish to know how much resistance 
(ohms) must be placed in a circuit to keep down the current 
flow to a certain limit, we need only divide the E. M. F. 
(volts) by the desired current (amperes) ; the result will be 
the value in ohms of the required resistance. 

Power. 

The power consumed or transmitted in an electric cir- 
cuit equals the product of the volts and amperes; pressure 
and current. 



POWER. IS 

To find the power of a steam engine, we must know the 
pressure of the steam and the quantity used; the power con- 
tained in the water of a dam depends upon its volume and its 
head. The power we can obtain from the wind depends upon 
its speed and the surface we expose to it which also measures 
the quantity. 

All of these cases are analogous and similar. Power ex- 
presses the rate of doing work, thus the rate of work is the 
same whether we are lifting one pound at the rate of 100 
feet per minute, or 100 pounds at the rate of one foot per 
minute. The unit of electrical power is the watt. It is the 
power expended in an electric circuit when one ampere flows 
through a resistance of one ohm, or when a difference of 
potential of one volt is maintained in a circuit having a resist- 
ance of one ohm. In an electric light circuit, for instance, 
as far as the power is concerned, it is immaterial whether 
each lamp requires 110 volts and Yz ampere, or 55 volts and 
one ampere, or 220 volts and J4 ampere. The power (watts) 
expended in an electric circuit is always equal to the volts 
multiplied by the amperes; thus, one ampere at 1,000 volts 
is equal to 100 amperes at 10 volts, or to 200 amperes at 5 
volts. In any power transmission whenever the pressure 
(volts) is lowered, the current (amperes) must be increased 
or the power (watts) will fall off, and, on the other hand, 
whenever the pressure is increased the current may be 
decreased. 

Instead of multiplying volts by amperes, we can find the 
power in an electric light circuit by multiplying the current by 
itself and then by the resistance; or the E. M. F. by itself and 
divide by the resistance. 

Thus knowing the volts and the amperes, we use the 
formula E X I=W. Knowing only the amperes and the 
ohms, we may use the formula, l 2 X R = W; and lastly, 



16 



MODERN ELECTRICAL CONSTRUCTION. 



knowing only the volts and ohms, we use the formula, 
EVR = W. 

In the above E stands for E. M. F., or volts ; I for current 
or amperes; and R for resistance or ohms. 



Divided Circuits. 

Currents of electricity always flow along the paths of 
least resistance just as currents of water do. Water, it is 
well known, will not flow over the top of a mill dam while 




Figure 3 

there is an opening alongside of it through which it can flow. 
If a barrel of water be provided with two openings, one 
large opening and one small, a much larger quantity will 
flow out through the large opening than through the small. 
This is because the resistance to the flow of water of the 
large opening is so much less than the resistance of the 
small opening. 

An electric current will act in just the same way; the 
conductor having the lesser resistance will carry the greater 
current. If we know the resistances of the different paths 
open to a certain current we can determine to a nicety how 
much current will flow in each. In Figure 3, which repre- 
sents diagramatically a battery of two cells and an electric 
circuit, the resistance of the two paths, a and b, is equal to 



DIVIDED CIRCUITS. 17 

10 ohms each, and the current will divide equally between 
them. If the resistance of a were 5 ohms, and that of b, 
10 ohms, two-thirds of the total current would pass through 
a and the one-third through b. 

In all such divided circuits, the current is always in- 
versely proportional to the resistance and the simplest way 
to find the current in each is to add the resistances of the two 
circuits; for instance as above, 5 plus 10 equals 15; now 
5/15 of this current will flow through the 10 ohms and 10/15 
of the current will flow through the 5 ohms. 

To determine the combined resistance of the two wires,. 
a and b, we need simply to consider them as made into one 
wire. If they, are both alike, they would, if made into one 
wire, be twice as large as either one is at present, and would 
then have only one-half as much resistance as either one had 
before; for the resistance of any conductor increases directly 
as its length, and decreases as the cross-section increases. 
The combined resistances of any two conductors can be found 
by multiplying their two resistances together and dividing 
this product by their sum. Thus, again taking the value 
of a and b as 10 ohms each, 10X10 equals 100, this divided 
by 10 plus 10 equals 5, which is the combined resistance of the 
two. 

If we have a large number of branch circuits as shown in 
Figure 4, which represents diagramatically an incandescent 



I 



flo» 

o* 



y 



x 



mmHim 



Figure 4 



electric light circuit of 12 lights (which is equal to 12 separate 
circuits, since each lamp really forms a circuit by itself), we 
can find the joint resistance of the 12 by proceeding as before; 
that is, multiplying together the resistance of the first and 



18 MODERN ELECTRICAL CONSTRUCTION. 

second lamp and dividing by the sum of these resistances ; next 
take the result so obtained (which is the combined resist- 
ance of the first two lamps) and with it multiply the resist- 
ance of the third lamp and divide by the sum as before. By 
repeating this operation and always treating the joint resist- 
ances already found as one circuit, the joint resistance of any 
number of such circuits can be found. Another and a very 
much quicker way consists in using the following formula : 
The joint resistance of any number of parallel circuits is 
equal to the reciprocal of the sum of the reciprocals. The 
reciprocal of any number is 1 divided by that number. If we 
have three circuits, having respectively 10, 20, and 30 ohms 
resistance, we proceed in the following way: The reciprocal 
of 10 is 1/10, of 20, 1/20, etc., the joint resistance, there- 
fore, is 1/10 plus 1/20 plus 1/30 equals 11/60, and 1 divided 
by this number which is 5 5/11. 

These methods are only necessary when the resistances 
are of different values. When all of them are alike, as is 
usual with incandescent lights, the resistance of one lamp 
needs only to be divided by the number of lamps to find the 
joint resistance. Thus, supposing each of the 12 lamps to 
have a resistance of 220 ohms, the joint resistance off the 
circuit would be 220/12 = 181/3. 



CHAPTER II. 
Electric Bells. 

We are now in a position to apply the electrical laws we 
have just discussed practically, and for this, purpose may 
take up electric bells and bell circuits. 

Figure 5 shows an electric bell, push button and battery, 
all connected up and complete. The action of the bell when 




Figure 5 

fully connected is as follows : Pressing the push button 
closes the circuit and current at once flows from the carbon 
pole marked + through the push button to the binding post 
A on the bell frame, thence along the fine wire W to the 
iron frame-work supporting the armature, B. This frame- 



20 MODERN ELECTRICAL CONSTRUCTION. 

work is in electrical connection with B. The armature, B, 
is provided with contact spring S, which normally rests 
against the adjusting screw, C. The current now passes from 
the contact spring to the adjusting screw and from it to the 
wire wound on the magnets, M, around the many turns of 
wire to the binding post, D, and back to the zinc pole of the 
battery marked — . 

The current circulating many times in the wire wound on 
the spools of M makes the iron cores magnetic so that they 
now attract the armature B. When this armature is at- 
tracted, it moves towards the magnets, M, and carries the 
small contact spring with it, thus breaking the connection be- 
tween C and S. 

This stops the current flow and the magnets, M, are at 
once demagnetized, thus releasing the armature B, which 
flies back and again closes the circuit at CS, this causes the 
armature to be attracted again and once more the circuit is 
broken. In this way the armature is made to strike the gong 
continuously while the circuit is kept closed at the push button. 
When the button is released, the circuit is permanently open 
and the bell at rest. 

In the figure there is shown only one cell, this, if a good 
form is selected, is sufficient for a new bell if the circuit is 
not long. When, however, the bell is used much the contact 
points are eaten away by the little sparks occurring every time 
the bell breaks the circuit. Dirt is also likely to gather on 
them and prevent good contact being made. Both of these 
factors add resistance to the circuit, and consequently 
lessen the current flow. 

We have seen before that the current equals the E. M. 
F. divided by the resistance, and in order to obtain the 
necessary current flow to operate the bell, we may either 
clean the contact points to lessen the resistance, or increase 
the E. M. F. by adding another cell in series with the first. 



ELECTRIC BELLS. 



21 



The latter expedient is by far the better, because it gives 
us a little surplus of power which is very useful to over- 
come variations in adjustment of the contact spring, loose 
contacts, dirt, etc. We should avoid using too many cells 
as well as not enough. If too many cells are used, there 



Q 

□ 



□ 



Q 

□ 



B=Z* 



in 



Figure 6 

will be much unnecessary damage done to contact points by 
the larger sparks. 

If the circuit is very long, the great length of wire will 
also provide additional resistance. This can be overcome in 
two ways, by increasing the E. M. F. as above, or by using 
larger wires. We have already seen that the larger the wire, 
the less will be its resistance. It is common practice to use 



22 MODERN ELECTRICAL CONSTRUCTION. 

No. 18 copper wire for all ordinary distances and for single 
bells. With large bell systems, it is customary to use No. 16 
or 14 for the main wire, which leads to all of the bells and 
may be called upon to supply several bells at the same time. 
Figure 6 shows a diagram of such a system and in case the 
three push buttons are used at the same time, three times as 
much current will flow in the main or battery wire a as in 
either of the other wires. 

We have seen before that currents of electricity divide 
among different circuits in the inverse ratio of their resist- 
ances. In other words, the circuit having the least resistance 
will carry the most current. If our bell system, Figure 6, 
be "grounded" at the two points x and y (i. e., bare wire in 
contact with metal parts of buildings which are connected 
together) the current instead of flowing through the longer 
circuit and the bell, will flow through the short circuit and 
leave it impossible to operate the bells. If the contacts, at 
x and y are poor, i. e., of high resistance, only a small part 
of the current will leak from one to the other. In such a 
case, the bells may work properly, but the battery will soon 
run down and there is a strong likelihood that one of the 
wires will be eaten away through electrolytic action. To 
prevent troubles of this kind, bell wires should be well in- 
sulated and kept away from pipes or metal parts of building. 
Damp places should also be avoided and special care is 
recommended for the battery wire a, Figure 6. For further 
information concerning diagrams, etc., of bell circuits the 
reader is referred to Wiring Diagrams and Descriptions by 
the authors of this work, Fred J. Drake & Co., Chicago. 

Bell wires are usually run along base boards, over picture 
mouldings, etc., in some cases they are also fished as explained 
further on. Batteries should be located in cool, dry places, 
where they are not liable to freeze, and where they are 
readily accessible as they must be kept nearly full of water 
and must be recharged from time to time. 



23 
The Telephone. 

The principle and action of the Bell telephone can be best 
explained by reference to Figure 7. In this figure, A repre- 
sents the transmitter, and B, the receiver. The essential 
parts of the transmitter are : the diaphragm, a; an electric 
circuit, containing a battery, b, and consisting of the wires, 
c, c 1 and partly wound upon an iron core, d. ' 

This electric circuit, it will be seen from the figure, con- 
nects with one pole to the diaphragm, a, and with the other 
to a small metal plate, e. Between the diaphragm, a (which 
is a plate of very thin iron), and the plate, e, there are many 
small pieces of carbon which complete the circuit. When 
now a party speaks into the mouthpiece of the transmitter, 





Figure 7 

the sound waves cause the diaphragm, a, to vibrate; the rate 
of vibration and character of the vibrations being an exact 
duplication of the voice speaking into it. These vibrations 
cause the small pieces of carbon between the diaphragm and 
the back plate to be alternately compressed and allowed to 
expand. Now the resistance of these carbon pieces is de- 
creased as they are tightly pressed together, and again in- 
creased when the pressure is released. Therefore the cur- 
rent of electricity flowing through them varies continuously 
while the diaphragm is in motion. 

This varying current circulates around the lower part 
of the iron core, d, and the two windings upon it form an 



24 



MODERN ELECTRICAL CONSTRUCTION. 



ordinary induction coil. Every variation of current strength 
in the circuit of the transmitter is by means of it reproduced 
in the circuit of the receiver, B. 

The essential parts of the telephone receiver are : The 
diaphragm f, very similar to that of the transmitter, the two 
magnets, g, and the electric circuit coming from the induction 
coil of the transmitter. The electric circuit, we have already 
seen, is traversed by electric currents exactly like those that 
flow in the circuit of the transmitter. These currents pass 
around electro-magnets, g, and attract the diaphragm, /, 
more or less strongly in proportion to the varying degrees of 
current strength. 

In this manner the diaphragm, f, of the receiver is made 
to vibrate in exact unison with that of the transmitter, and 
thus to reproduce exactly the sounds given to the trans- 
mitter. 

The transmitter is not absolutely necessary for the re- 




Figure 8 

reiver can be used as such, and in fact was so used at first. 
Lines of short distances can be operated without transmit- 
ters, but the speech will not be as plain. 



INDUCTION COIL. 



25 



Figure 8 is a diagram of the connections of two telephone 
instruments together with the necessary call bells. When the 
lines are not in use, the receivers, a, are hanging on the 
hooks, h, holding them down as shown by dotted lines. This 
leaves the circuit complete through the earth, g, magneto 
generator, e, bell f, line i, and duplicates of these parts at the 
right. When now the magneto generator is operated both 
bells will ring. When the receivers are removed, a spring 
forces the hook upwards making the connection shown in 
solid lines. This closes the battery circuit which must be 
open when the instrument is not in use or the battery wilj 
run down. 

The talking circuit is now complete from earth, g, through 
the receiver, a, induction coil, b, line i, and duplicates of these 
parts at the right. 



The Induction Coil. 

Figure 9 is a diagramatic illustration of an induction 
coil as used mostly by medical men. Such an instrument 




Figure 9 

consists of an iron core, B, usually made up of a number 
of soft iron wires ; and two electrical circuits insulated from 
each other, and terminating in the two pair of binding posts, 
A and D. Of these two circuits A consists of a short length 



26 MODERN ELECTRICAL CONSTRUCTION. 

of comparatively heavy, wire wound upon the iron core, and 
is known as the primary coil. D is a similar coil, but usually 
consisting of many more turns of wire, and the wire is also of 
much smaller gauge and is known as the secondary coil. 

The operation is as follows : A battery is connected to the 
binding posts, A, and current begins to flow in the circuit. In 
this circuit is an interrupter or vibrator, E, constructed 
similarly to the one described in connection with the electric 
bell. As current flows through the primary coil, it mag- 
netizes the core, B, and this attracts the armature, E, causing 
it to break the connection between itself and the adjusting 
screw. As this connection is broken, the current in A ceases 
to flow, the core is de-magnetized and the armature again 
connects with the adjusting screw. This action is repeated 
just as in the electric bell, and in consequence the core B, 
is rapidly magnetized and de-magnetized. 

Every time the core, B, is magnetized a current of electric- 
ity, lasting, however, only an instant, is induced in the second- 
ary coil, D. The magnetism in the core is caused by a cur- 
rent of electricity circulating around it, and currents of 
electricity are in turn produced by this magnetism in the 
other or secondary coil. 

This method of producing electric currents is known as 
electro-magnetic induction, and currents so produced are said 
to be "induced" currents, hence the name induction coil. The 
currents so induced are alternating, that is, changing in 
direction. At the ''making" of the primary circuit, the cur- 
rent in the secondary coil is in a direction which opposes the 
magnetization of the core by the primary current; at the time 
of "break" in the primary circuit, the induced current will be 
in the opposite direction. 

The tube, C, is movable and may be slipped entirely in over 
the iron core, or withdrawn entirely. If it is in, the currents 
which were before being induced in the secondary wires are 



BATTERIES 



27 



now induced in the metal of the tube and consequently the 
effect on the secondaries is very much reduced. 

The energy in the primary and secondary coils is always 
equal. If the two coils have the same number of turns, the 
currents and electro-motive forces are exactly alike. If the 
secondary coil has more turns of wire than the primary, 
the induced E. M. F. in it will be greater, but the current 
will be smaller and vice versa. The induction coil is ver> 
similar to the alternating current transformer, the maij 
difference being that the transformer does not have an in- 
terrupter since the current supplied to it is itself constantly 
alternating. 



Batteries. 

Currents of electricity for commercial purposes are pro- 
duced either by dynamo electric machines or by batteries. 

A "battery" is the name given to a number of cells con- 
nected together so as to produce a current greater than one 





Figure 10 



Figure 11 



cell alone could produce. Figure 10 shows one cell of a kind 
that is generally used only intermittently, as for instance with 
door-bells. When the bell is not ringing the battery is idle. 



28 MODERN ELECTRICAL CONSTRUCTION. 

This style of cell is very useful for such work, but entirely 
useless for work requiring current continuously. The cell 
consists of a glass jar which is filled about % full of water 
in which a quantity of sal-ammoniac is dissolved. Immersed in 
this solution is a carbon cup or center, which forms the 
positive or + pole of the cell, and a zinc rod, carefully 
separated from the carbon by a rubber washer at the bottom 
and a porcelain tube at the top. So arranged, the current tends 
to flow, in the battery, from the zinc to the carbon and if the 
zinc and carbon outside of the cell be joined by a piece of 
wire or other conductor of electricity, the current will flow 
in the external circuit, from the carbon back to the zinc. If 
the zinc and carbon are not joined by a conductor of electric- 
ity there will be no current flow, but merely an electrical pres- 
sure tending to send a current. Each cell of this kind has 
an electro-motive force of about 1.4 volts. This is not suffic- 
ient for general use in connection with bells, etc., and in 
order to obtain greater current strength a number of cells 
are connected together in series as shown in Figure 11. 

This figure shows a different kind of cell, but will never- 
theless illustrate the method of connecting cells in series; 
which is, to connect the carbon or copper pole of the first 
cell to the zinc of the second, and again the carbon pole of the 
second to the zinc of the third, continuing in this way through 
all of the cells. Thus connected, all of the electro-motive 
forces act in one direction and if we have twelve cells each 
of an electro-motive force of 1.4 volts, we obtain a total 
electro-motive force to apply on our work of 12 X 1.4 or 16.8 
volts. 

Shoula we, however, connect six of the twelve cells as 
above, and then accidentally connect the other six in the 
opposite direction, that is, the zinc of the sixth cell to the 
zinc of the seventh, and then continue in this order, we should 
obtain no current whatever; six of our cells would tend to 



BATTERIES. 29 

send current in one direction and six in the other, so that the 
result would be nothing. Should ten cells be properly con- 
nected to send current in one direction and' two connected 
to oppose them, the net electro-motive force would be 10 X 1.4 
minus 2 X 1.4, which is 11.2. The ten cells would force current 
through the other two in the opposite direction. 

The electro-motive force of a cell is independent of its 
size, that is, a very small cell would set up just as high an 
electrical pressure as a very large one made of the same 
material. A large cell is, however, capable of delivering a 
much stronger current because its own resistance to the cur- 
rent flow is much less than that of a small cell. Large cells 
will, therefore, in most cases give very much better service 
than small ones. Especially in cases where considerable 
current is required as in electric gas-lighting and annunciator 
work, where it is always possible that two or three bells or 
fixtures may be called into action at the same time. 

In setting up and maintaining sal-ammoniac batteries, the 
following general rules should be observed : 

Use only as much sal-ammoniac as will readily be dis- 
solved; if any settles at the bottom it shows that too much 
has been used. Keep your battery in a cool place, but do 
not allow it to freeze. See that the jars are always about 
Y\ full of water. 

Keep the tops of glass jars covered with paraffin to 
prevent salts from creeping. 

The battery should never be allowed to remain in action 
(i. e., send current) continuously, or it will run down. If 
it has been run down through a short circuit or other cause, 
it should be left in open circuit for several hours ; it will then 
usually "pick up" again. 

The so-called dry-batteries are made up of about the 
same material, but applied in form of a paste. They are 



30 MODERN ELECTRICAL CONSTRUCTION. 

suitable for the same kind of work and especially handy for 
portable use. 

For continuous current work, such as telegraphy, for 
instance, the kind of battery shown in Figure 11 is generally 
used. The electro-motive force of this style of battery is a 
little less than that of the sal-ammoniac battery and its re- 
sistance is considerably greater. 

Therefore, it is not well adapted for work requiring con- 
siderable current strength. Bells, telegraph instruments, etc., 
to be used with this battery require to be specially designed 
for it; the current being less in quantity must be made to 
circulate around the magnets many more times in order to 
fully magnetize them. 

The sal-ammoniac batteries cannot be used continually or 
they will run down ; this battery must be kept at work always 
or it will deteriorate. 

This style of cell is known as the crow-foot or gravity 
cell, the action of gravity being depended upon to separate 
the essential elements of the solution. 

To set up this battery, the zinc crow-foot is suspended 
from the top of the glass jar as shown. The other element 
of the cell consists of copper strips riveted together and 
connected to a rubber-covered wire shown at the left of each 
cell, Figure 11. This copper is spread out on the bottom of 
the jar and clear water poured in until it covers the zinc. 
Next drop in small lumps of blue vitriol, about six or eight 
ounces to each cell. 

The resistance may be reduced and the battery be made 
immediately available by drawing about half a pint of the 
upper solution from a battery already in use and pouring it 
into the jar; or, when this cannot be done, by putting into 
the liquid four or five ounces of pulverized sulphate of zinc. 

Blue vitriol should be dropped into the jar as it is con- 
sumed, care being taken that it goes to the bottom. The 



BATTERIES. 



31 



r 



i 



*\ 



need of the blue vitriol is shown by the fading of the blue 
color, which should be kept as high as the top of the copper, 
but should never reach the zinc. 

A battery of this kind when newly set up should be short 
circuited for a few hours, that is, a wire should be con- 
nected from the zinc at one end of the battery to the copper 
at the other. 

There are many styles of batteries and different chemicals 
are used with them. The two kinds above described are, 
however, the most used. The methods of connecting is in 
all batteries the same. 

Figure 12 shows a diagram of a battery connected in 

series; the long thin lines repre- 
sent the copper or carbon pole 
from which the current flows in 
the external circuit and the short 
thick lines represent the zinc from 
which the current flows toward 
the copper inside of the cell. 
If we have a circuit of low resistance to work through 
and desire to increase the current, we may group our cells as 

shown in Figure 13, where two 
sets are in parallel. This arrange- 
ment will give a stronger current, 
but it is necessary to see that both 
groups of cells have the same 
electro-motive force; if they have 
not, the higher one will send the 
current through the lower. If the two batteries are not con- 
nected with similar poles together, they would be on short cir- 
cuit, and no current could be obtained in the external circuit. 



Figure 12 



E 


t* - r 


** 


HI BB 




hi sa 


J 




«, + v 




Figure 13 





CHAPTER III. 

Wiring Systems. 

There are numerous systems of electric light distribution. 
The oldest and the first to come into general use is shown 
diagramatically in Figure 14. This is the series arc system. 
In this system the same current passes through all of the 
lamps; and as more or less lamps are required the E. M. F. 
of the dynamo must be correspondingly increased or dimin- 

\>s ^/ \ / \ / v/ \/ 



• \ /"s 7\ 7\ s\ 



\ 



/\ S\ 7\ 7^ 7X 7\ 

Figure 14 

ished. This is accomplished by means of an automatic 
regulator connected to the dynamo. 

The current used with this system seldom exceeds ten 
amperes and large wires are never required. This system is 
best suited for street lighting where long distances are to be 
covered. 

In these diagrams, D represents the dynamo, and F, 
the "field" coils of the dynamo. With constant current 
systems the "fields" are usually in series with the armature 
of the dynamo, as shown in Fig. 14, and the lamps, so 
that the same current must pass through all. With constant 



WIRING SYSTEMS. 



33 



potential systems, the field coils are generally independent of 
the rest of the circuit. With such systems the current used 
in the circuit is so variable that it cannot be used in the 
fields. 

Another system, known as the multiple arc or parallel 
system, is shown in Figure 15. In this system the E. M. 
F. never varies, but the current is always proportional to the 








O 



Figure 15 

number of lights used. If, for instance, only one light is used, 
there is a current of about one-half ampere, but if ten 16 
cp. lights are used there must be a current of about five 
amperes. Where many lights are used with this system, the 
main wires require to be quite large, and must always be 
proportional to the number of lights. This system is oper- 
ated usually at 110 volts and is suitable for residences, stores, 
factories and all indoor illumination. It is not well adapted 
to the transmission of light and power over long distances. 
The 3-wire system shown in Figure 16 combines many of 




A Vi A A A A A 



LLLLLOJ 



Figure 16 

the advantages of both the foregoing systems. As will be 
seen from the diagram, it consists of two dynamos connected 
in series and a system of wiring of one positive +, one nega- 
tive — and a neutral = wire. So long as an equal number of 



34 



MODERN ELECTRICAL CONSTRUCTION. 



lights are burning on both sides of the neutral wire, this 
wire carries no current, but should more lights be in use 
on one side of the system than on the other, the neutral wire 
will be called upon to carry the difference. If all the lights 
on one side are out, the dynamo on that side will be running 
idle. 

The currents in the neutral wire may be either positive 
or negative in direction. The principal advantage of this sys- 
tem is that with it double the voltage of the 2-wire systems 
is employed and yet the voltage at any lamp is no greater than 
with the use of two wires. It is customary to use 110 volts 
on each side of the neutral wire and this gives a total volt- 
age over the two outside wires of 220 volts. As the same 
current passes ordinarily through two lamps in series, we 
need, for a given number of lamps only half as much current 
as with 2-wire systems and can, therefore, use smaller 
wires. For the same number of lights and the same per- 







Figure 17 

centage of loss the amount of copper required in the two 
outside wires is only one-fourth that of 2-wire systems; to 
this must be added a third wire of equal size for the neutral, 
so that the total amount of copper required with this system 
is Y% of that of 2-wire system using the same kind of lamps. 
Incandescent lamps are often run in multiple-series, as in 



WIRING SYSTEMS. 



35 



Figure 17, without a neutral wire. The number of lamps to 
be used in series depends upon the voltage of the dynamo. 
If that is 550, five 110 volt lamps are required in each group, 
or ten 55 volt lamps. 

If the filament of one lamp breaks all of the lamps in 



Q3ZIJ 



<> 



-o- 
-o- 



mm 



Figure 18 

that group are extinguished and if one is to be used all must 
be used. 

Figure 18 shows the diagram of a series-multiple system. 
This style of wiring should be avoided. 

A diagram of an alternating current system is shown in 



ow 



i 






m 



Figure 19 

Figure 19. In this system extremely high voltage is used and 
consequently the currents are never very great. This makes 



36 MODERN ELECTRICAL CONSTRUCTION. 

it extremely useful for long distance transmission. Since, 
however, the high pressure employed cannot be used directly 
in our lamps it must be transformed into lower pressure. 
This is done by means of transformers, and it is possible to 
reduce the line voltage to any desirable extent. As the volt- 
age is reduced, however, the current increases and the wires 
taken from the transformers into the buildings must be as 
large as those for 2-wire systems using the same kind of 
lamps. The high pressure, or primary wires, are rarely 
allowed inside of buildings. 

The Transmission of Electrical Energy. 

We have seen that currents of electricity flow only in 
electrical conductors, and that these conductors are usually 
arranged in the form of wires. We have further seen that 
the power transmitted is proportional to the product of the 
volts and amperes used. The actual amount of energy trans- 
mitted being the product of the above multiplied by the time. 

Currents of electricity always encounter some resistance 
and in consequence of this resistance, generate heat; the 
generation of heat in any electric circuit being proportional 
to the square of the current multiplied by the resistance. 
This formula, I 2 X R expresses the loss of electrical energy 
due to the resistance of the conductors and which reappears 
in the form of heat. If this loss is not kept within reasonable 
limits, the wires will become very hot and destroy the in- 
sulation or ignite surrounding inflammable material. The 
above loss and hazard is generally guarded against by insur- 
ance companies and inspection boards by designation of the 
current in amperes which certain wires may be allowed to 
earry. 

Table No. 1 gives the currents which the National Board 
of Fire Underwriters has decided to consider safe and which 



ELECTRICAL TRANSMISSION 37 

should be closely followed, and on no account should wires 
smaller than those indicated be used. There is no harm and 
no objection to using wires larger than indicated, but neither 
is there much gained unless the run be a long one as we shall 
see further on. 

The table of carrying capacities shows a great discrepancy 
between the relative cross-section of large and small wires 
and the currents they are allowed to carry; thus a No. 0000 
wire has a cross-section about eight times as great as that of 
No. 6, yet is allowed to carry less than five times as much. 

This discrepancy arises from the different rate of heat 
radiation. The radiating surface or circumference of a small 
circle or wire is relatively to its cross-section much greater 
than that of a large circle, and other things being equal the 
ratio existing between the heat given to a body and its radiat- 
ing surface determine its temperature. 

We have seen before that the power (either for lights or 
motors) consists of two factors; current and pressure, ex- 
pressed respectively as amperes and volts. We have also seen 
that the power (watts) equals the product of these two; 
hence it follows, that as we increase either one, we may de- 
crease the other, or conversely, as one is decreased the other 
must be increased in order to deliver a given amount of 
power. We further know that it is the current alone which 
heats the wires and that accordingly as our currents are large 
or small, the wires used to transmit them must be large or 
small. It is obvious, therefore, that we can save much on 
copper by using higher voltages, since, if we double the 
voltage, we shall need only one-half as much current and can, 
therefore, use a much smaller wire. As an example : Sup- 
pose we have power to transmit which at 110 volts requires 
90 amperes. This requires a No. 2 wire containing 66,370 
circular mils. Now, if we double the voltage, we shall need 
only 45 amperes; this much we are allowed to transmit over 



38 MODERN ELECTRICAL CONSTRUCTION. 

a No. 6 wire which has only 26,250 circular mils. We must 
not, however, increase our voltage without due precaution and 
consideration, for high voltage is dangerous to life and in- 
creases the fire hazard. It also increases the liability to 
leakage and requires better and more expensive insulation 
which in a small measure offsets the other advantages. The 
usual voltage employed at present varies from 110 to 220 
volts for indoor lighting and power; 500 to 650 volts for 
street railway work and from 2 to 20,000 volts for long 
distance transmission. The higher voltages mentioned are 
seldom brought into buildings, and are nearly always used 
with some transforming device which reduces the pressure to 
110 or 220 volts for indoor lighting or power. 

The flow of current through a given lamp, motor, or re- 
sistance determines the light, power or heat obtainable from 
such device. We know that the flow of current in turn 
(other things being equal) varies as the E. M. F. maintained 
at the terminals of any of these devices. Consequently in 
order to obtain a steady flow of current it is necessary to 
provide a steady E. M. F. 

The loss of E. M. F. in any wire is equal to the current 
flowing in that wire multiplied by the resistance of the wire. 
Since it is impossible to obtain wires without resistance, it 
is also impossible to establish a circuit without loss and 
wherever electricity is used some loss must be reckoned with. 
We may make this loss as large or as small as we desire. 
Where the cost of fuel is high, it is important to keep this 
loss quite small, using for that purpose larger wires. On the 
other hand where there is an abundance of cheap fuel, or, 
where, for instance, water power is used, it will be more 
economical to waste five or ten per cent of the electrical 
energy than to spend the money needed to provide the copper 
necessary to reduce the waste to one or two per cent. 

In this connection, however, it must not be overlooked that 



ELECTRICAL TRANSMISSION 39 

the quality of the service depends to a great extent upon the 
loss allowed and here the nature of the business supplied must 
be taken into consideration. In yards, warehouses, barns, 
etc., a variation of five or ten per cent in candle power may 
not matter much, but in residences or offices it is very 
annoying. 

The loss in voltage depends, as we have already seen, 
upon the current used, and the resistance of the wire em- 
ployed. If the current is decided upon, we can reduce the loss 
only by reducing the resistance; the resistance can be re- 
duced only by increasing the size of wire used. If we double 
the cross-section of the wire, we decrease the resistance one- 
half and consequently reduce the loss or variation in volt- 
age one-half. Thus it will be seen that as we attempt to 
reduce the loss in voltage to a minimum we shall require 
very large wires and thus greatly increase the cost of our 
installation. 

For instance, if a line be in operation with a loss ->f 
twenty per cent, by doubling the amount of copper, we reduce 
the loss to ten per cent. In order to reduce our loss to five 
per cent, we must again double the amount of copper; and 
to reduce the loss still more, say to 2y 2 per cent, a wire 
of double the cross-section of the last must be used. If the 
cost of copper in the original installation utilizing eighty per 
cent of the energy be taken as 1, then the cost of copper to 
utilize ninety per cent will be 2; of ninety-five per cent, 4; 
and of ninety-seven and one-half per cent, 8; and no amount 
of copper will ever be able to save the full 100 per cent. 
We must not overlook, however, that although a reduction of 
loss from four to two per cent requires us to double the 
amount of copper, it does not necessarily double the cost of 
our installation, for in many cases it adds but a small per- 
centage to the total cost. For instance, if it were decided to 
use No. 12 instead of No. 14 wire in moulding or insulator 



40 MODERN ELECTRICAL CONSTRUCTION. 

work, the cost of labor would not be appreciably affected 
thereby; similarily in connection with a pole line, the dif- 
ference in total cost occasioned by the use of say No. 6 
instead of No. 10 wire would be small. 



Calculation of Wires. 

In electrical calculations so far as they relate to wiring, 
the circular mil plays an important part, and it becomes 
necessary to thoroughly understand its meaning. The mil 
is the 1/1000 part of an inch, consequently one square inch 
contains 1,000x1,000 equals 1,000,000 square mils. If all elec- 
trical conductors were made in rectangular form, we should 
be able to get along nicely by the use of the square mil, but, 
since they are nearly all in circular form, the use of the square 
mil as a unit would necessitate otherwise unnecessary figures. 
The circular mil means the cross-section of a circle one mil 
in diameter, whereas the square mil means a square each 
side of which is equal to one mil in length. Square mils, 
can, therefore, be transformed into circular mils by dividing 
by .7854, and circular mils into square mils by multiplying 
by .7854, since it is well known that a circle which can be 
inscribed within a square bears to that square the ratio of 
.7854 to 1. 

To illustrate: Using square mils if we wish to determine 
the cross-section of a wire having a diameter of 50 mils, we 
must first square the diameter and then multiply by .7854; 
50 X 50 X .7854, or 1963.5, which is the cross section of the 
wire expressed in square mils. To express the cross-section 
in circular mils, we have but to square the diameter, or 50 X 
50 = 2500 circular mils. The 2500 circular mils are exactly 
equal to the 1963.5 square mils. The adoption of the circular 
mil simply eliminates the figure .7854 from the calculations. 

The resistance of a copper wire having a cross-section of 



CALCULATION OF WIRES 4 * 

one mil and a length of one foot is from 10.7 to 10.8 ohms, 
Jie variation being due to the temperature of the wire. 10.8 
ohms is the resistance usually taken. This resistance in- 
creases directly as the length and decreases as the cross-sec- 
tion increases. The resistance of any copper wire can, there- 
fore, be found by multiplying its length by 10.8 and dividing 
by the number of circular mils it contains. Expressed in 

L X 10.8 

formula this becomes R = ■ where L stands for the 

C. M. 
total length of wire in feet, and C. M. for the cross-section 
in circular mils, and R for the resistance in ohms. In 
order to find the loss in volts, we must multiply the resistance 
by the current used. Representing this current by I, the 
I X L X 10.8 

formula becomes = V; V being the volts lost. 

C. M. 

It is, however, seldom necessary to find how many volts would 
be lost with a certain wire and current, but rather to find how 
many circular mils are necessary in a wire so that the volts lost 
may not exceed a certain percentage. In order to determine this, 
we transpose V and C. M. and the formula now becomes 
I X L X 10.8 

= C. M. This is the final formula and gives 

V 
directly the number of circular mils a wire must have so that 
the loss with this current and length of wire shall not exceed 
the limits set by V. 

As an example, we have a current of 20 amperes to trans- 
mit a distance of 200 feet and the !qss shall not exceed 
two per cent; voltage 110. This requires 400 feet of wire 
(two wires 200 feet long) and two per cent of 110 is 2.2. We 
therefore have 20 X 400 X 10.8 divided by 2.2, which gives 
us 39,270 circular mils, which we see by table I is a little less 
than a No. 4 wire. 



42 MODERN ELECTRICAL CONSTRUCTION. 

The above formula will answer for all 2-wire work, 
whether it be lights or power. 

It is simply necessary to find the current required with 
whatever devices are to be used. 

These calculations are not often made in actual practice. 
It is much easier to refer to tables such as II. Ill, IV, V, VI, 
given at the end of this volume, by which the proper size 
of wire can be determined at a glance almost. 

In connection with 3-wire systems using two lamps in 
series, we need to calculate the two outside wires only, the 
neutral wire should then be taken of the same size. We must 
however assume double the voltage existing on either side 
of the neutral; that is to say, a 2-wire system using 110 volts 
would be figured at 110 volts, while a 3-wire system, using 
110 volt lamps on each side of the neutral wire would be 
figured at 220 volts. 

It must also be noted that with 3-wire systems the cur- 
rent required is only y 2 of that required with 2-wire sys- 
tems. Ordinarily we have two lamps in series and the same 
current passes through both. Applying this to our formula 
we see that with the 3-wire system the current I is only half 
as great as with 2-wire systems and (the percentage of loss 
in both cases being the same) V, which stands for the volts 
to be lost, becomes twice as great. Owing to these two fac- 
tors, the wire for 3-wire systems need have only % as many 
circular mils as that of a 2-wire system with the same per- 
centage of loss. To this must be added the neutral wire so 
that the total cost of wire must be Y% of that for the 2-wire 
systems. 

The amount of copper required in power transmission for 
a given percentage of loss varies as the square of the voltage 
employed. By doubling the voltage we can transmit power 
with the same loss four times as far; or, if we do not change 
distance or wire, we shall have only one-fourth of the loss 



CALCULATION OF WIRES 43 

we had before. A practical idea of the laws governing the 
distribution of circuits and the losses in voltage and wire 
which are unavoidable may be gained from Figure 20. 

Figure 20 shows 96 incandescent lights arranged on one 
floor and placed 10 feet apart each way. With all cutouts 
placed at A and circuits arranged as in No. 1, 2,080 feet of 
branch wiring for the eight circuits of 12 lights each, will be 
required. If the cutouts be placed in the center, B, the same 
length of wire will be necessary. We have in this case merely 
transferred the cross wires from one end of the hall to the 
center. If we arrange two sets of cutouts as at C and D 
and run circuits as 3 and 4 the total amount of wire necessary 
will be only 1,920 feet. By this arrangement we avoid the 
necessity of crossing the space indicated by dotted lines at 
the right, opposite B. 

If we run the circuits on the plan of No. 2, the least amount 
of wire for the eight circuits will be 2,560 ft. Such wir- 
ing would require extra wires feeding the various groups. 
Should we run a set of mains along ACBD, and make 12 
circuits of the installation by placing one cutout for each 
eight lights, the amount of wire required will be 1,680 feet. 
If we run a set of mains through B as shown by dotted lines 
using 12 lights per circuit, 1,760 feet of wire will be re- 
quired. If we now double the number of lights in the same 
space or limit the number per circuit to six, we shall require 
3,200 feet of wire to feed them all from A, but only 2,400 to 
feed them from B ; to feed them all from the two centers C 
and D will also require 2,400 feet. 

The most economical location of cutout centers will, with 
even distribution of light, and in regard to branch wiring 
only, be such that it is unnecessary to iun circuits like No. 2; 
in other words, not more than the number of lights allowed on 
one circuit should lead away from it in one direction. 

Suppose, for instance, the number of lights be increased 



44 



MODERN ELECTRICAL CONSTRUCTION. 



lo 



Sc 



id 



so 



§ 



o o 



§c : c 



so kd 



o o 



• «z 



R 






M 



S^ 



CNi 



Figure 20 



ft 



/09.3.7 /09-2 5 



n n — n 



□ a ~o 



OX UZTE Q Q O 



Q Q m 



d — g 



oYi b id 

® 
Sqq P 



D 



/07.96 

o o 



CALCULATION OF WIRES 45 

i 

bj one-half or (which amounts to the same thing in wire), 
the number of lights per circuit be limited to eight. If we 
run all branch circuits from A, we shall need a total of 2,760 
feet. It will require just as much wire to run the 64 lights 
below X as was required to run the whole 96 before; viz.: 
2,080 feet ; to this must be added the wire necessary to run the 
four circuits above which is 680 feet. By extending our 
mains to the point X, we can save eight runs of wire each 
equal in length to the distance between A and X. X is the 
point of extreme economy as regards branch wires and nothing 
can be gained in this respect by extending the mains any 
further unless several cutout centers are decided upon as 
before explained. Whether it be more economical to extend 
the mains to X, or run branch circuits from A, depends upon 
the relative cost, in this instance, of 30 feet of mains and 
480 feet of branch wires. 

With an uneven distribution of lights as indicated by the 
black circles, each of which may be taken as an arc lamp or 
cluster of incandescent lamps, the most economical location 
of cutouts will be at Z. To move them farther to the right 
would shorten the wires of five circuits and lengthen them on 
eight; to move either up or down in the group of eight would 
also lenghten more wires than it would shorten. 

In laying out circuits for electric lights, however, we 
must not take into consideration the cost of wire only. In 
many cases the loss in voltage is of far greater importance, 
not only because it means a steady waste of power, but also 
because of unsatisfactory illumination, lamps in different 
parts of a circuit not being of the same candle power, or 
the light in one place varying greatly when lights in another 
place are turned on or off. 

Some idea of the variation in voltage in different parts 
of differently arranged circuits can be obtained from Figure 20. 
The length of wire in circuit 1 is 35 feet to the first lamp and 



46 MODERN ELECTRICAL CONSTRUCTION. 

10 feet from this to the next, etc. The voltage at the cut- 
out A is 110 and at each lamp is given the actual voltage 
existing at that point with all lamps burning. The wire of 
the circuit is No. 14 and with 55 watt lamps, the loss to the 
last lamp over a run of 145 feet is a trifle over two and one- 
half per cent when all lamps are burning. 

Circuit No. 2 is figured as of the same length as No. 1, 
and supplies the same number of lamps, but at a much greater 
loss, slightly over four per cent to the last lamp. Circuits 3 
and 4 feeding from C contain equal lengths of wire, but 
there is quite a difference in loss; in 3 only .75 of one volt, 
while in 4 it is a little over two volts. From study of Figure 
20 we may learn that the arrangement of circuit 1 is fairly 
satisfactory especially if the nature of the work done under 
it is such that only part of the lamps are used at the same 
time. Circuit No. 2 is bad if all lights are used at once, and 
it should be wired with No. 10 or 12 wire. Whenever the loca- 
tion of lights is such as to allow a circuit like No. 3 to be run, 
the loss can be kept very low with a minimum of wire. In 
general the more cutout centers there are established in propor- 
tion to the number of lights, if mains are properly arranged, 
the less will be the loss in pressure and the more satisfactory 
the service. 



NOTICE.— DO NOT FAIL TO SEE WHETHER ANY 
RULE OR ORDINANCE OF YOUR CITY CONFLICTS 
WITH THESE RULES. 



Class A. 
STATIONS AND DYNAMO ROOMS. 

Includes Central Stations, Dynamo, Motor and Storage- 
Battery Rooms, Transformer Substations, Etc. 

1. Generators. 

a. Must be located in a dry place. 

It is suggested that water proof covers be provided, which may 
be used iu case of emergency. 

Perfect insulation in electrical apparatus requires that the 
material used for insulation be kept dry. While in the con- 
struction of generators the greatest care is taken that all cur- 
rent carrying parts are well insulated, still, if moisture is al- 
lowed to settle on the insulation, trouble is almost sure to oc- 
cur. For this reason a generator should never be installed 
where it will be exposed to steam or damp air or in any place 
where through accident water may be thrown against it. A 
location under steam or water pipes or close to an outside win- 
dow should be avoided. 

b. Must never be placed in a room where any hazardous 
process is carried on, nor in places where they would be ex- 
posed to inflammable gases or flyings of combustible materials. 

In even the best constructed dynamos there is alyays more 
or less sparking at the brushes and small pieces of hot carbon 



48 MODERN ELECTRICAL CONSTRUCTION. 

are sometimes thrown off. As a general rule in buildings 
where there is considerable dust, such as in wood-working 
plants, grain elevators and the like, the dynamo is located in 
the engine room, which is generally isolated from the dusty 
part of the building. 

c. Must, when operating at a potential in excess of 550 
volts, have their base frames permanently and effectively 
grounded. 

Must, when operating at a potential of 550 volts or less, 
be thoroughly insulated from the ground wherever feasible. 
Wooden base frames used for this purpose, and wooden floors 
which are depended upon for insulation where, for any rea- 
son, it is necessary to omit the base frames, must be kept filled 
to prevent absorption of moisture and must be kept clean and 
dry. 

Where frame insulation is impracticable, the Inspection 
Department having jurisdiction may, in writing, permit its 
omission, in which case the frame must be permanently and 
effectively grounded. 

If desired, high potential machines may be surrounded by an 
insulated platform, made of wood, mounted on insulating supports, 
and so arranged that a man must always stand upon it in order to 
touch any part of the machine. 

Under ordinary circumstances it is better to insulate the 
base frames of generators. Excessive voltages are often pro- 
duced in the windings, as for instance, where the field circuits 
are opened, and unusual electrical strains result. A generator 
with an insulated base frame is, therefore, less liable to trouble 
from grounds than one in which the base frame is in electrical 
connection with the ground. 

Where generators operate at high . voltages, however, the 
question of life hazard must be considered. If the base frame 
is insulated from the ground there is always the possibility 
that a person touching it may receive a severe shock and for 
this reason it is deemed advisable to ground all generator 
frames where the voltage generated is over 550 volts. 



GENERATORS. 



49 



The smaller generators are usually insulated on wooden 
base frames. A base frame suitable for this work is shown in 
Figure 21. Almost any kind of wood, well varnished, is very 
good for this purpose. The base frame is screwed to the floor 
or foundation and the slide rail (which is used where the 
dynamo is belted to the engine to allow the tightening and 
slackening of the belt) is independently attached to it, that is, 
the same bolt must not be used to hold the slide rail to the 




Figure 21. 



Figure 22. 



base frame and the base frame to the floor, as this would be 
liable to ground the frame. The direct connected machines 
(dynamo and engine on same bed plate) are often insulated 
by the use of mica washers and bushings surrounding the bolts 
which fasten the dynamo to the bed plate and by using an in- 
sulated flange coupling between the shaft of the dynamo and 
that of the engine. Figure 22 shows a section of a flange 
coupling insulated in this way, the heavily shaded parts rep- 
resenting the insulating material. 

The larger machines, which on account of their weight 



50 



MODERN ELECTRICAL CONSTRUCTION. 



cannot be insulated, must be permanently and effectually 
grounded. Where the engine and dynamo are direct con- 
nected a very good ground is obtained through the engine con- 
nections. Where belts are used a good ground can be obtained 
by fastening a copper wire under one of the bolts on the dy- 
namo and connecting the other end of the wire to available 
water pipes. 

In the case of high tension machines, especially series arc, 
the. machine should always be surrounded by an insulated 
platform so arranged that a man must stand on it in order to 




Figure 23. 



touch any part of the machine, either live parts or frame, and 
in handling such a machine only one hand at a time should 
be used. A hardwood platform mounted on insulators will 
serve very well for this purpose or suitable platforms may be 
obtained from dealers in electrical supplies. 

Figure 23 shows a metallic comb such as is occasionally 
used to overcome the static electricity due to the friction of 
the belt. A strip of metal, one end of which is cut with a 
number of projecting points, is suspended crosswise a short 



GENERATORS. 5 1 

distance above the belt. A wire connects this plate to any 
suitable ground. 

A resistance for grounding the generator frame in accord- 
ance with this rule is constructed of ground glass equipped 
with two metal terminals separated a short distance and con- 
nected by means of a lead pencil mark. One terminal is con- 
nected to the frame of the -machine and the other to the 
ground. 

d. Constant potential generators, except alternating cur- 
rent machines and their exciters, must be protected from ex- 
cessive current by safety fuses or equivalent devices of ap- 
proved design. 

For two-wire, direct-current generators, single pole protection 
will be considered as satisfying the above rule, provided the safety 
device is located in the lead not connected to the series winding. 
When supplying three-wire systems, the generators must be so 
arranged that these protective devices will come in the outside 
leads. 

For three-wire, direct-current generators, a safety device must 
be placed in each armature, direct-current lead, or a double pole, 
double trip circuit breaker in each outside generator lead and cor- 
responding equalizer connection. 

Constant potential generators are designed to carry a 
certain amount of current without seriously overheating. If 
any considerable overload is put on a machine of this type a 
dangerous rise in the temperature of the generator and the 
wires connected to it will occur and a fire may result. To 
protect the apparatus some safety device must be installed in 
the main circuit which will cut off the current when it exceeds 
its normal maximum value. The safety fuse is commonly 
used for this purpose, but circuit breakers of approved de- 
sign meet the requirements of the rule and may be used in 
place of the fuses. 

Alternating current generators are usally constructed in 
large units. If a safety device installed in the main circuit of 
one of these large machines should operate and open the cir- 
cuit, the generating apparatus, dynamo and engine would mo- 



52 



MODERN ELECTRICAL CONSTRUCTION. 



mentarily be left in a dangerous condition owing to the fact 
of the load being suddenly rerrtoved from the generator. 

The sudden disrupting of the circuit of an alternating cur- 
rent generator gives rise to a momentary, excessive increase 
in the E. M. F., and as this is usually already very high there 
is great tendency to pierce the insulation of the generator 
winding. 

In view of these facts, and for the further reason that on 
short circuit the impedance of an alternating current armature 
consisting of many coils in series is generally of such an 






A 



OvNA 

B 



Figure 24. 



amount as to limit the resultant current, alternating current 
generators are excepted from the general rule requiring pro- 
tection by safety devices. While the rule does not require 
protective devices in any alternating current generator, still 
it is the general practice, and it is advisable, to provide 
fuses or circuit breakers on the smaller size generators such as 
are used in isolated plants for instance. 

Fuses are sometimes mounted on the generator itself, but 
the general practice at the present time is to mount all fuses 
on the switchboard. For two-wire, direct current generators 



GENERATORS. 



53 



one fuse will suffice, provided this fuse is located in the lead 
which is not connected to the series winding. The diagram 
Figure 24 shows the proper location of the fuses. An inspec- 
tion of this diagram will also show the reason for this re- 
quirement. Two compound wound generators are shown con- 
nected in parallel. To avoid confusion the shunt field and 
switch connections are not shown. When the generators are 
operating together current from the brush on the right-hand 
side of machine A has two paths by means of which it can 
get to the positive bus bar. One of these paths is through its 
own series field and the other through the equalizer connection 



Own. 



o^ 



/wO 



ywQ- 



Figure 25. 



and series field of generator B. The current in the lead con- 
nected to the series field may not be of as great strength as 
that generated in the armature; or, due to the fact that it 
may be receiving additional current from the other machine 
through the equalizer connection, it may be of greater strength 
than that generated in the armature. A fuse placed in this 
lead could not, therefore, provide proper protection for the 
armature. 

Where a shunt wound generator is used the fuse may be 
placed in either lead. The same is true in the case of a single, 
compound wound generator, for no equalizer connection is 



54 



MODERN ELECTRICAL CONSTRUCTION. 



used in this case, and the current in both leads is always the 
same. 

Where generators are feeding a three-wire system the fuses 
should be placed in those leads which feed into the positive 
and negative mains, Figure 25. They should not be placed in 
the equalizer lead or in the lead connected to the series field 
for the reasons already given. It will be noticed that the 
two generators shown at the right of the diagram are con- 
nected in a reverse manner from those at the left. An ex- 
amination of the diagram, Figure 26, will show the reason for 



•Ch^ Own, 



QwJ K3vv\ 



Figure 2G. 



this. In this case the placing of the fuse in the lead not 
affected by the equalizer current brings it in the lead con- 
nected to the neutral bus. If, with the fuse located in this 
line, the generator winding should become grounded a short 
circuit would result, as the neutral wire is always grounded, 
current flowing from the positive bus bar through the positive 
lead and the wires on the generator to the ground. The gen- 
erator would have absolutely no protection in a case of this 
kind and a fire would be sure to result. If the fuses were 
placed in the outside leads the circuits would be immediately 
opened and current shut off from the machine. 



GENERATORS. 



55 



Figures 27, 28 and 29 show the proper location of fuses 
in three-wire, direct current generator installations. In Fig- 
ure 2/ is shown the wiring connection of a three-wire direct 
current generator. The armature of this generator contains 
two separate armature windings, each winding being provided 
with its own commutator, located on each side of the arma- 
ture. Two separate series field windings are provided, each 



r-VWv 



fAAAA-U 




Figure 27. 



field winding being connected in series with an armature wind- 
ing. The shunt field connections are not shown. 

To comply with the requirements each generator should 
be connected to the bus bars and fuses installed as shown. 
The simplified diagram, Figure 30, shows the reason for this 
arrangement. Referring to the connections shown it will be 
seen that the fuses protect each armature winding both from 
overload or from possible shorts caused by the grounding of 
the armature windings. A wrong arrangement of the fuses, 
and one that should be avoided, is shown in the diagram. 
Figure 31. In this case fuses are installed in the lead from 



56 



MODERN ELECTRICAL CONSTRUCTION. 



the series winding. The first objection to this arrangement 
is the one which has already been explained, i. e., the cur- 
rent from the armature having two paths open to it, one 
through the series field and one through the equalizer, the 
armature could generate an excessive current without the 
fuse, which may be carrying only a part of the current, blow- 
ing. If for any reason one of the fuses shown did blow seri- 
ous conditions might result owing to the fact that the arma- 




Figure 28. 



ture of that machine is still connected to the armatures of all 
the remaining machines through the equalizer bus. A double- 
pole circuit breaker so arranged as to open both the series 
field lead and the equalizer lead would remove this objec- 
tion, but, as the circuit breaker would be actuated by the cur- 
rent in the series field lead the objections before stated still 
exist. Locating the fuse in the armature lead connected to the 
neutral bus would leave the generator unprotected in case of 
grounds. 

Figure 28 shows the connections of the Westinghouse direct 



GENERATORS. 



57 



current, three-wire generator. In this generator direct cur- 
rent at the potential of the outside mains, usually 220 voits, 
is taken off the commutator side while the neutral connection 
is made through auto transformers to slip rings on the opposite 
side of the armature shaft. Two separate series field windings 
are connected in series with each direct current armature lead. 
In order to place a fuse in each direct current armature lead, 
fuses would have to be mounted on the generator itself or the 




00 LLD 



Figure 29. 



leads would have to be carried from the armature brushes to 
the switchboard and back to the series field. The usual pro- 
tection provided with this generator consists of double-pole, 
double-trip circuit breakers connected in the leads from the 
series fields and corresponding equalizer connection, this cir- 
cuit breaker being actuated by the current in the lead from 
the series field and arranged to open both series field and 
equalizer leads. As this generator is designed to withstand 
only a 25 per cent overload the circuit breakers should be 



58 MODERN ELECTRICAL CONSTRUCTION. 

interconnected so that in case one generator lead opens it 
automatically opens the remaining lead. 

Figure 29 shows the wiring connections of 3 compensator 
set. This set consists of two machines, the armature shafts of 
which are rigidly connected together. Each machine acts as 
a motor or generator, depending on the condition of unbal- 
ance ; and they are used only to balance the system, other gen- 
erators supplying current to the outside mains. 

This class of apparatus is protected in the same manner 
as in the case just described. A double-pole, double-trip cir- 
cuit breaker should be installed in each outside lead and cor- 



tttz 



_c 

± 



Figure 30. Figure 31. 

responding equalizer lead. It might be well to state that with 
apparatus designed on the principle just described various 
details of construction of the machines, as built by the dif- 
ferent manufacturers, require a more complicated system of 
protection so that the above rule is not always exactly com- 
plied with. 

Circuit breakers, when used for protection in dynamo 
leads, are generally mounted on the switchboard and con- 
nected in the circuit ahead of the main switch. The circuit 
breaker as at present constructed is, in nearly all cases, a 
much more efficient and reliable device than the fuse, and its 
use is to be recommended. The fusing point of an ordinary 



GENERATORS. 59 

fuse depends on the temperature of the fuse metal. When 
fuses are used in an engine room where the temperature is 
often very high the fuse may blow when it is carrying a cur- 
rent very much less than its rated capacity, and this will gen- 
erally result in a larger fuse being installed. The circuit 
breaker is not affected by this increase in temperature. When 
a fuse blows from overload it generally occurs at a time when 
all the appartus is in use and serious delays are apt to result 
before the fuse can be replaced. This objection does not exist 
where the circuit breaker is used. 

As to the relative currents at which the fuse and circuit 
breaker should be set to operate, authorities differ. Some ad- 
vise that both be set to operate at the same current strength 
so that the fuse, which takes a longer time to operate, will 
blow only in case the circuit breaker fails. Another recom- 
mends that the fuses be of such capacity as to carry any load 
which will be required of them and to set the circuit breaker 
a little higher than the fuses so that the fuses will operate on 
overload and the circuit breaker on short circuit. The prac- 
tice of setting the fuses at about 25 per cent above the circuit 
breaker seems to be preferred, for it frequently happens, when 
both are set to operate at the same current strength, the fuse 
alone will "blow," due to the excessive heat produced in the 
fuse at full load. 

There is a tendency in the design of some of the newer 
generators to do away with binding posts, leads properly 
bushed through the generator frame and arranged for direct 
connection to leads from switchboard being provided instead. 
As this does away with exposed, live parts it is to be recom- 
mended. Where there are exposed live parts on the genera- 
tor or its connections they should be protected from accidental 
contact, except where they are at the same potential as the 
ground, as in the case of the neutrals on the direct current 
three-wire systems and the ground return on trolley systems. 



60 MODERN ELECTRICAL CONSTRUCTION. 

Cases are sometimes found where the cessation of current 
due to the blowing of a fuse could cause more damage than 
would result from on overload, as, for instance, where the 
dynamo operates some safety device. In cases of this kind the 
Inspection Department having jurisdiction may modify the 
requirements. 

e. Must each be provided with a name-plate, giving the 
maker's name, the capacity in volts and amperes, and the 
normal speed in revolutions per minute. 

f. Terminal blocks when used on generators must be 
made of approved non-combustible, non-absorptive insulating 
material, such as slate, marble or porcelain. 

g. The use of soft rubber bushings to protect the lead 
wires coming through the frames of generators is permitted, 
except when installed where oils, grease, oily vapors or other 
substances known to have rapid, deleterious effect on rubber, 
are present in such quantities and in such proximity to motor 
or dynamo as may cause such bushings to be liable to rapid 
destruction. In such cases hardwood properly filled, or pre- 
ferably porcelain or micanite bushings must be used. 

2. Conductors. 

(For construction rules see Nos. 49 to 57.) 

From generators to switchboards, rheostats or other in- 
struments, and thence to outside lines : — 

a. Must be in plain sight or readily accessible. 

Wires from generator to switchboard may, however, be 
placed in a run-way in the brick or cement pier on which 
the generator stands. When protection against moisture is 
necessary, lead covered cable or iron conduit must be used. 

b. Must have an approved insulating covering as called 
for by rules in Class "C" for similar work except that in 
central stations, on exposed circuits, the wire which is used 
must have a heavy braided, non-combustible outer covering. 

Bus-bars may be made of bare metal. 
Where a number of wires are brought close together, as 
is generally the case in dynamo rooms, especially about the 



CONDUCTORS. 6l 

switchboard, they must be surrounded with a tight, non-com- 
bustible outer cover. 

Flame proofing must be stripped back on all cables a suf- 
ficient amount to give the necessary insulation distances for 
the voltage of the circuit on which the cable is used. 

c. Must, when not in a conduit, be kept so rigidly in 
place that they cannot come in contact. 

d. Must in all other respects be installed with the same 
precautions as required by rules in Class "C" for wires carry- 
ing a current of the same volume and potential. 

e. In wiring switchboards, the ground detector voltmeter, 
pilot lights and potential transformers must be connected to 
a circuit of not less than No. 14 B. & S. gage wire that 
is protected by an approved fuse, this circuit is not to carry 
over 660 watts. 

For the protection of instruments and pilot lights on 
switchboards, approved N. E. Code Standard Enclosed Fuses 
are preferred, but approved enclosed fuses of other designs 
of not over two (2) amperes capacity, may be used. 

A number of different methods are used for running wires 
in dynamo rooms. Where the dynamo is located in a room 
with a low ceiling, or where it is not desirable to run the 
wires open, metal conduits may be imbedded in the floor and 
the wires run in them. If the engine room is located in the 
basement or in any place where water or moisture is liable 
to gather on the wires, lead covered wires must be used or the 
wires must be run in iron conduit. It is permissible to install 
an ordinary braided rubber covered wire or cable without a 
lead covering in iron conduit, but in this case the greatest care 
should be taken that all joints in the conduit system are well 
leaded and well made so that the conduit system when installed 
will be water tight. In most installations the generator leads 
are not protected by fuses and a short circuit in them is very 
liable to result in a fire. The reliability of the whole plant is 
also dependent on the generator leads so that it is generally 
advisable, where moisture is present, to use lead covered wires 
or cables for generator leads. At outlets the conduits should 



62 MODERN ELECTRICAL CONSTRUCTION. 

be carried some distance above the floor level and close to the 
frame of the ma-chine, where the wires will be protected from 
mechanical injury. If the space under the machine will allow 
it, the conduit should be ended there where it will be protected 
by the base frame. Where lead covered wires are used, the 
lead should be cut back some distance from the exposed part 
of the wire and the end of the lead should be well taped and 
compounded so that no moisture can creep in between the lead 
and the insulation. 

In place of the metal conduits tile ducts can be used; or, if 
the floor is of cement, a channel may be left in the floor and 
the wires run into it. A removable iron cover should be 
provided. 

The wires may be run open on knobs or cleats as described 
in Class C. Where there are many wires, cable racks, con- 
structed of wood or preferably iron, having cleats bolted to 
them, may be used. As a general rule moulding should not 
be used for this class of work. Especially in central stations 
the generators are often called upon for a very heavy overload 
and should the wires become overheated a fire is much more 
apt to result when the leads are run in moulding than if they 
were run open where any trouble could be immediately 
noticed. 

The bringing together of a number of wires, as frequently 
occurs in dynamo rooms, presents a distinct fire hazard un- 
less some means is taken to protect the wires in case of fire. 
The rubber insulation of wires is very inflammable and a 
quantity of it burning, not only causes a hot fire but also pro- 
duces a considerable amount of dense smoke. For the protec- 
tion of rubber covered wires the outer braid may be flameproof 
or a non-combustible tubing may be slipped over the ordinary 
braided wire. If either of these is used care must be taken 
to strip them back some distance from the copper as they 
are absorbent and moisture will be sure to cause grounds. 



SWITCHBOARDS. 63 

For the wiring on the back of the switchboard slow-burning 
wire may be used. 

3. Switchboards. 

a. Must be so placed as to reduce to a minimum the 
danger of communicating fire to adjacent combustible mate- 
rial. 

Switchboards must not be built up to the ceiling, a space 
of three feet being left, if possible, between the ceiling and 
the board. The space back of the board must be kept clear 
of rubbish and not used for storage purposes. 

b. Must be made of non-combustible material or of hard- 
wood in skeleton form, filled to prevent absorption of moist- 
ture. 

If wood is used all wires and all current carrying parts 
of the apparatus om the switchboard must be separated there- 
from by non-combustible, non-absorptive, insulating material. 

c. Must be accessible from all sides when the connections 
are on the back, but may be placed against a brick or stone 
wall when the wiring is entirely on the face. 

If the wiring is on the back, there must be a clear space 
of at least eighteen inches between the wall and the apparatus 
on the board, and even if the wiring is entirely on the face, 
it is much better to have the board set out from the wall. 

d. Must be kept free from moisture. 

The switchboard may be located in any suitable place in 
the dynamo room but never placed in close 1 proximity to com- 
bustible material or where, if a fire did start, it would be liable 
to communicate to surrounding walls. It should generally be 
placed in a central position as close as possible, without in- 
convenience, to all machines and perfectly accessible. Do not 
locate a switchboard under or near a steam or water pipe or 
too close to windows, as in such locations the board may at 
any time become wet. 

The switchboard may be made of hardwood in skeleton 
form (See Figure 32), but in this case all switches, cutouts, 
instruments, etc., must be mounted on non-combustible, non- 



6 4 



MODERN ELECTRICAL CONSTRUCTION. 



absorbtive, insulating bases, such as slate or marble, and all 
wires must be properly bushed where they pass through the 
wood work and must be supported on cleats or knobs. Wood 
base instruments are not approved. 

The wood switchboard is fast becoming obsolete, modern 



01 



I ! UJ 



o 

< 
Z 

>• t 
D 



a 







Figure 32. 



switchboards being constructed of slate or marble slabs. These 
slabs must be free from metallic veins, for if these are present 
they may cause considerable leakage of current which will 
manifest itself by heating. 

The marble or slate slab is supported in an angle iron 



SWITCHBOARDS. 65 

frame so constructed as to support and substantially brace the 
slab. The metal frame should preferably, for low potential 
work, be. insulated from the gound by mounting on wood or 
marble blocks ; this, however, not being demanded by the Un- 
derwriters' rules. 

The switchboards should be so arranged that all switches 
and other operating devices are in easy reach and the rear of 
the board should be free from unnecessary crossing of bus 
bars and other conductors. In designing a switchboard spe- 
cial attention should be paid to the manner in which the con- 
ductors are brought to the board and the bus bar work should 
be so laid out as to require the minimum amount of exposed 
rubber covered conductors. 

It is well to keep all lights used for decorative or illum- 
inating purposes entirely off the board as these complicate the 
wiring. Plenty of light should be provided both at front and 
rear of the board but these should be supplied by separate 
wiring. 

Wires, or wires and bus bars, of opposite polarity should 
in no case come in contact and where liable to come in contact 
should be rigidly supported. All parts of the board should 
be easily accessible for inspection and repairs. A separation 
should be maintained between bus bars and conductors and any 
grounded metal part of the board. This separation should be 
as great as possible and in no case less than one-half inch. 

Bus bars should be of ample carrying capacity. While the 
Code does not specify any particular carrying capacity for bus 
bars, this being considered more of an engineering feature as 
these bars are not surrounded by the usual combustible insulat- 
ing material, still they should be of ample size. A bus bar 
that heats is liable to communicate heat to the fuses and cause 
them to blow below their designed capacity. Sizes and carry- 
ing capacities of bus bars commonly used are as follows : 



66 



MODERN ELECTRICAL CONSTRUCTION. 



Thickness of 

Bus Bar Carrying Capacity 

% inch 1,000 amperes per sq^. in. 

% inch 800 amperes per sq. in. 

Y% inch 700 amperes per sq. in. 

J/2 inch 600 amperes per sq. in. 

For bolted connections between copper bus bars an area of 
one square inch is generally allowed for each 150 amperes. 





Figure 33. 



This will, however, vary with different manufacturers from 
100 to 200 amperes per square inch. 

The code calls for a minimum spacing of 18 inch between 



RESISTANCE BOXES AND EQUALIZERS. 67 

the apparatus on the back of the board and the wall. This is 
often misinterpreted to apply to the marble slab and not to 
the apparatus on the back of the board, with the result that 
there is little or no free space at the back of the board when 
the bus bars and other apparatus is put in place. It is of the 
utmost importance for the personal safety of any one who has 
to work at the back of the board, especially when the board 
is alive, that sufficient space be provided and at least three 
feet should always be allowed where possible. 

As there is a great temptation to use the space back of the 
board for storage purposes it is quite common practice to pro- 
vide an iron grating surrounding the board and to place locks 
on the doors so that access can be obtained only by those 
authorized. 

Figure 33 shows the front and rear views of a modern 
switchboard. 

4. Resistance Boxes and Equalizers. 

(For construction rules see Nos. 78 and 79.) 

a. Must be placed on a switchboard, or at a distance of 
at least one foot from combustible material or separated 
therefrom by a slab or panel of non-combustible, non-ab- 
sorptive, insulating material such as slate, soapstone or marble, 
somewhat larger than the rheostat, which must be secured 
in position independently of the rheostat supports. Bolts for 
supporting the rheostat shall be countersunk at least one- 
eighth inch below the surface at the back of the slab and 
filled. For proper mechanical strength, slab should be of a 
thickness consistent with the size and weight of the rheostat, 
and in no case to be less than one-half inch. 

If resistance devices are installed in rooms where dust or 
combustible flyings would be liable to accumulate on them, 
they must be equipped with dust-proof face plates. 

Resistance boxes or rheostats are used for a great variety 
of purposes in electrical work. The Code is concerned mostly 
with that class of resistance box used with light or power 



68 MODERN ELECTRICAL CONSTRUCTION. 

work where more or less heat is developed. The more com- 
mon uses of resistance boxes are given below and in each of 
these cases the device must be installed in accordance with the 
foregoing rules : starting boxes for motors, speed controllers 
for motors including elevator starters and the like, field 
rheostats for both motors and dynamos, resistances used in 
series with arc and mercury vapor lamps and theater dimmers. 

On central stations where current is furnished over a large 
area there is on some of the circuits, especially the long ones, 
a considerable "drop," or loss of potential. In order to keep 
the voltage at the point of supply on these circuits at the 
proper value, the voltage at the station must be raised. This 
in turn causes the voltage on those circuits near the dynamo 
to become excessive. Equalizers, which are large resistance 
boxes generally constructed of iron wire or strips and capable 
of carrying a heavy current, are connected in the circuits and 
adjusted at such resistances as to make the voltage at the 
various points of supply uniform. They are generally too 
heavy to mount on the board, but should be raised on non- 
combustible, non-absorptive insulating supports and should be 
separated from all combustible material. 

Starting boxes and speed controllers are resistance boxes 
connected in a motor circuit and so arranged that the amount 
of resistance can be varied. The resistance coils are mounted 
in an iron case with a slate or marble front on which are 
placed the terminals. Dynamo field rheostats are generally 
mounted on the back of the marble switchboard, a small hand 
wheel being provided so that the rheostat can be operated from 
the front of the board. If the switch board is of wood in 
skeleton form, or if the rheostat is placed on a wall or other 
support of combustible material, it should be mounted on a 
solid piece of slate or marble. Separate screws should be used 
for attaching the rheostat to the slate or marble and the slate 
or marble to the wall for, if the same screws were used for 



RESISTANCE BOXES AND EQUALIZERS. 



69 



this purpose they would be liable to ground the frame of the 
rheostat or might conduct heat to the material to which the 
rheostat is fastened. The method of fastening is shown in 
Figure 34 and this applies also to other forms of rheostats. 




Figure 34 



b. Where protective resistances are necessary in con- 
nection with automatic rheostats, incandescent lamps may be 
used, provided that they do not carry or control the main 
current nor constitute the regulating resistance of the device. 

When so used, lamps must be mounted in porcelain re- 
ceptacles upon non-combustible supports, and must be so 
arranged that they cannot have impressed upon them a volt- 
age greater than that for which they are rated. They must 
in all cases be provided with a name-plate, which shall be 
permanently attached beside the porcelain receptacle or re- 
ceptacles and stamped with the candle-power and voltage 
of the lamp or lamps to be used in each receptacle. 

Automatic rheostats are arranged to control a motor auto- 
matically, usually from some point remote from the apparatus 
itself, this action being generally obtained by the use of 
solenoids. 

The simplified diagram Figure 35 will show the manner in 
which this device operates. When the switch A is closed the 
solenoid B immediately draws up the core, at the lower end of 
which is attached a contact piece. The main circuit is then 
closed through the motor and resistance, this resistance being 



70 



MODERN ELECTRICAL CONSTRUCTION. 



gradually cut out of circuit as the core moves up and the, motor 
comes up to speed. It is very evident that considerable cur- 
rent will be required in the solenoid to draw up the core and 
contact piece and that much less current will be needed to 
hold it in place after it has completed its travel. As the time 
of operation is short the heating effect due to the current in 
the solenoid circuit will not have any serious effect, but if the 
current was left on for any great length of time the coil would 




Figure 35. 



be liable to burn out. To prevent this and also a waste of 
energy the protective resistance of the incandescent lamp L is 
cut into the solenoid circuit when the core has moved to its 
highest point by the opening of the contacts shown just below 
the lamp at C. 

c. Wherever insulated wire is used for connection between 
resistances and the contact plate of a rheostat, the insulation 



LIGHTNING ARRESTERS. Jl 

must be "slow burning." For large field rheostats and sim- 
ilar resistances, where the contact plates are not mounted 
upon them, the connecting wires may be run together in 
groups so arranged that the maximum difference of potential 
between any two wires in a group shall not exceed 75 volts. 
Each group of wires must either be mounted on non-com- 
bustible, non-absorptive insulators giving at least one-half 
inch separation from surface wired over, or, where it is nec- 
essary to protect the wires from mechanical injury or moist- 
ure, be run in approved lined conduit or equivalent. 

The resistance element of large field rheostats, starting de- 
vices and speed controllers are sometimes mounted separately 
from the contact plates, the segments on the contact plates 
being connected to their respective resistances by wires. If 
the resistance element is placed near the contact plate the wires 
may be run between the two on insulating supports. Where 
this cannot be done, or where the wires are liable to mechan- 
ical disturbance they may be grouped and run in lined conduit 
or in unlined conduit if encased in fibrous flexible conduit. 

Slow burning insulation is demanded on all wires which 
connect to a rheostat. This class of insulation is much less 
liable to take fire from an overhead rheostat than the ordi- 
nary rubber covered wire, but while its heat resisting quali- 
ties are good its insulating qualities are rather poor so that un- 
der no circumstances should the difference of potential be- 
tween any two wires in a group, whether the wires are run 
open or in conduit, exceed 75 volts. The added insulation 
of the lined conduit, or the flexible tubing or the insulating 
supports are necessary as it is possible to have the full differ- 
ence of potential of>the system existing between any one of the 
wires and the ground. 

5. Lightning Arresters. 

(For construction rules see No. 82.) 

a. Must be attached to each wire of every overhead cir- 
cuit connected with the station. 



J2 MODERN ELECTRICAL CONSTRUCTION. 

b. Must be located in readily accessible places away from 
combustible materials, and as near as practicable to the 
point where the wires enter the buildings. 

In all cases, kinks, coils and sharp bends in the wires be- 
tween the arresters and the outdoor lines must be avoided 
as far as possible. 

c. Must be connected with a thoroughly good and per- 
manent ground connection by metallic strips or wires having 
a conductivity not less than that of a No. 6 B. & S. gage 
copper wire, which must be run as nearly in a straight line 
as possible from the arresters to the ground connection. 

Ground wires for lightning arresters must not be attached 
to gas pipes within the buildings nor be run inside of iron 
pipes. 

d. All choke coils or other attachments, inherent to the 
lightning protection equipment, shall have an insulation from 
the ground or other conductors equal at least to the insula- 
tion demanded at other points of the circuit in the station. 

A lightning discharge is simply a discharge of electricity at 
very high potential. While the insulation of the ordinary wire 

serves very well for the voltages 
_ for which it is designed it offers 

very little resistance to a current 
of such high potential, and, pro- 
viding the discharge can reach the 
ground by jumping through the 



LINE 



WWWWVWVVV 



Gaojn d 



insulation, it will generally take 
that course unless some easier path 
is offered to it. A lightning ar- 
rester in its simplest form consists 

Figure 36. °^ tw0 meta ^ plates separated by a 

small air space as shown in Fig- 
ure 36. One of the plates is con- 
nected to the line and the other to the ground, a set being pro- 
vided for each line wire to be protected. 

The air space between the metal plates offers a much lower 
resistance to the passage of this high potential than do the 



CARE AND ATTENDANCE. ?$ 

magnets of a dynamo, for instance, or highly insulated parts 
of the line. The current, therefore, jumps the air space and 
passes to ground. When the current jumps this air space it 
produces an arc similar to that of an arc lamp, and after the 
lightning discharge is over the dynamo current is very likely 
to maintain this arc and thus cause a short circuit from one 
lightning arrester through the ground to the other. Different 
methods of preventing this by interrupting the arc have been 
devised. 

Figure 2>7 shows the T. H. lightning arrester, in which 
the arc is extinguished by a magnetic field set up by the elec- 
tro-magnet. In the non-arcing lightning arrester (Figure 38) 
the discharge takes place across the air gaps between the 
cylinders. 

A choke coil is simply a coil of wire, the size of wire and 
the number of turns depending upon the normal current and 
voltage of the systehi on which it is used. On 500 volt street 
railway circuits the choke coil sometimes consists of a spiral 
of five or six turns of heavy copper rod, while on high po- 
tential, alternating current circuits a greater number of turns 
and smaller wire is used. As every coil of wire has a certain 
amount of inductance, or, in other words, tends to hold back 
any change in the E. M. F., the placing of a coil in the cir- 
cuit between the lightning arrester and the apparatus on which 
the current is used affords a protection to the apparatus and 
forces the lightning discharge to pass to the ground through 
the lightning arrester. 

As the lightning arrester and choke coil are subjected to 
extremely high potentials they should be carefully insulated 
and properly located. 

6. Care and Attendance. 

a. A competent man must be kept on duty where gen- 
erators are operating. 



74 



MODERN ELECTRICAL CONSTRUCTION. 



b. Oily waste must be kept in approved waste cans and 
removed daily. 

7. Testing of Insulation Resistance. 

a. All circuits except such as are permanently grounded 
in accordance with No. 15 must be provided with reliable 
ground detectors. Detectors which indicate continuously and 
give an instant and permanent indication of a ground are 
preferable. Ground wires from detectors must not be attached 
to gas pipes within the building. 

b. Where continuously indicating detectors are not feasi- 




Figure 37. 

ble the circuits should be tested at least once per day, and 
preferably oftener. 

The exceptions to this rule are 3-wire direct current sys- 
tems where the neutral is grounded and 2 and 3 wire alter- 
nating current secondaries where the neutral or one side is 
grounded. 



TESTING. 



75 



In every installation of electric wiring there is a certain 
"leak" of current. This leak is partly between the wires and 
the ground and between the wires themselves. The amount of 
leak varies, but is always dependent on the insulation resist- 
ance. Where a small amount of wire is well installed the leak 
should be very small, but in the case of large installations 



R 



*S 



H 



8» * « 



JEk CTi Q P 0. 




n — in — nr 



eS 



•4 



n — d — u 



4 



Qtound 



Figure 38. 



or where the wiring has been poorly done the flow of current 
to ground or between the wires of opposite polarity may be- 
come quite large. Wires lying on pipes or on damp wood- 
work, crossed wires or live parts of apparatus mounted on 
wooden blocks, all tend to cut down the insulation resistance 
and increase the leak. The effects of poor insulation are : 



76 



MODERN ELECTRICAL CONSTRUCTION. 



First, it represents a useless loss of current, and, second, and 
more important, it means a possible cause of fire. 

The simplest way to determine the insulation resistance of 
a circuit is by means of a voltmeter. In Figure 39 if a volt- 
meter of known resistance is connected between one side of 
the circuit and the ground and there is a ground on the other 
side of the circuit, say at X, current will flow from the positive 
wire through the voltmeter, then through the ground at X to 
the negative side of the circuit. The voltmeter needle will 
indicate a certain reading which we will call V 1 . If the volt- 
meter is now connected directly across the circuit we get the 
circuit voltage, which we will call V. The two readings, V 1 , 
and V, are to each other as the resistance of the voltmeter 
is to the combined resistance of the voltmeter and the ground 
at X ; or, calling the resistance of the voltmeter R and the re- 
sistance of the ground at X r, we get 

V 1 R V - V 1 

— = , or r = R 

V R + r V 1 

As an example : On a certain system the voltage across the 
mains is no, while with the voltmeter connected as shown in 



£ 








Figure 39. 



Figure 40. 



Figure 39 we obtain a reading of 38. The resistance of the 
voltmeter is 10,500 ohms. Supplying the numbers in the for- 



TESTING. 



77 



mula, r = 10,500 X 



110-30 



30 



28,000 ohms as the resistance to 



ground the negative side of the system. If the voltmeter is 
connected to ground from the other side, or — main, the resist- 
ance to ground of the + side can be obtained. 

If both sides of the system are grounded as at x and y, 
Figure 40, the voltmeter will be robbed of part of the current 
which would pass through it if Y were not in parallel with it. 
It will therefore not indicate correctly under such circum- 
stances. If Y for instance were a very good ground the 
voltmeter would give no indication whatever of the ground at x. 
If, however, tests are frequently made and defects cleared 
up at once when noticed it will seldom happen that two 

grounds occur on the system at the 
same time. An engineer or dynamo 
tender will soon learn what the in- 
sulation resistance of the plant in his 
charge should be and be governed 
accordingly. 

A diagram of a direct current 
ground detector switch is shown in 
Figure 41. By throwing switch A 
down the — bus bar is connected to 
the ground through the voltmeter 
and by throwing switch B the -f- bar 
is connected to ground through me 
|k] | voltmeter. The ground wire should 

Figure 41. be run to a water or steam pipe 

(never to a gas pipe) or to some grounded part of the build- 
ing. If no good ground is obtainable one may be made as 
described under 15 g. 




/8 MODERN ELECTRICAL CONSTRUCTION. 

8. Motors. 

a. Must, when operating at a potential in excess of 550 
volts, have no exposed live metal parts and have their base 
frames permanently and effectively grounded. 

Motors operating at a potential of 550 volts or less must 
be thoroughly insulated from the ground wherever feasible. 
Wooden base frames used for this purpose, and wooden B 
floors, which are depended upon for insulation where, for 
any reason, it is necessary to omit the base frames, must be 
kept filled to prevent absorption of moisture, and must be 
kept clean and dry. Where frame insulation is impracticable, 
the Inspection Department having jurisdiction may, in writ- 
ing, permit its omission in which case the frame must be 
permanently and effectively grounded. 

If desired, high-potential machines may be surrounded with an 
insulated platform made of wood, mounted on insulating supports, 
and so arranged that a man must stand upon it in order to touch 
any part of the machine. 

Where motors with grounded frames are operated on sys- 
tems where one side is either purposely or accidentally 
grounded there exists a certain difference of potential between 
the windings and the motor frame, this difference of poten- 
tial depending on the part of the circuit considered. At some 
places in the winding it will be the full difference of po- 
tential at which the motor is operating and at other points 
practically nothing. Should the conductors accidentally come 
in contact or "ground" on the motor frame a short circuit 
would result, as the circuit would then be completed through 
the motor frame and ground. To obviate this the motor frame 
should be insulated from the ground. This may be done either 
by setting the motor on a wood floor or by the use of a base 
frame, as with generators. A base frame should always be 
used where possible, for when a motor is set directly on the 
floor it is often impossible to keep the space under it clean, 
and there is always a liability of the floor being damp or of 
nails in the floor passing through the woodwork into some 
grounded part of the building or metal piping. A properly 



MOTORS. 79 

constructed base frame will allow of easy cleaning of the space 
under the motor. 

In the case of elevator or other motors where the shunt 
field is suddenly broken, a momentarily high voltage is induced 
in the field windings. If the frame of the motor is grounded 
this high voltage has a strong tendency to jump through the 
insulation of the wires to the metal work of the motor, thus 
grounding the circuit. 

b. Motors operating at a potential of 550 volts or less 
must be wired with the same precautions as required by rules 
in Class "C" for wires carrying a current of the same volume. 

Motors operating at a potential between 550 and 3,500 
volts must be wired with approved multiple conductor, metal 
sheathed cable in approved unlined metal conduit firmly se- 
cured in place. The metal sheath must be permanently and 
effectively grounded, and the construction and installation of 
the conduit must conform to rules for interior conduits (See 
No. 28), except that at outlets approved outlet bushings shall 
be used. 

The motor leads or branch circuits must be designed to 
carry a current at least 25 per cent greater than that for 
which the motor is rated. Where the wires under this rule 
would be overfused in order to provide for the starting cur- 
rent, as in the case of many of the alternating current motors, 
the wires must be of such size as to be properly protected by 
these larger fuses. 

The current used in determining the size of varying speed 
alternating current motor leads or branch circuits must be 
the percentage of the 30-minute current rating of the motor 
as given for the several classification of service in the fol- 
lowing table : — 

Percentage of 
Classification of Services. current rating 

of motor. 
Operating valves, raising or lowering rolls, tool 

heads, etc 200 

Hoists, rolls, ore and coal-handling machines.. 180 

Freight elevators, shop cranes 160 

Passenger elevators 140 

Rolling tables, pumps 120 



80 MODERN ELECTRICAL CONSTRUCTION. 

Varying speed motors are motors in which the speed varies auto- 
matically with the load, decreasing when the load increases, and 
vice versa. It does not mean motors in which the speed is varied 
by the use of different windings or grouping of windings, or motors 
in which the speed is varied by external means, and in which, after 
adjusting to a certain speed, the speed remains practically constant. 

The insulation of the several conductors for high potential 
motors, where leaving the metal sheath at outlets, must be 
thoroughly protected from moisture and mechanical injury. 
This may be accomplished by means of a pot head or some 
equivalent method. The conduit must be substantially bonded 
to the metal casings of all fittings and apparatus connected 
to the inside high tension circuit. 

Where outside wires direcly enter the motor room the In- 
spection Department having jurisdiction may permit the wires 
for high potential motors to be installed according to the 
general rules for high potential systems. 

Good values to use for calculating the size of wire for 
branch conductors are given below. The question of loss of 
voltage is not taken into consideration here. 

no volts 9.3 amperes per horsepower 

220 volts 4.6 amperes per horsepower 

500 volts 2 amperes per horsepower 

For mains supplying many motors it is not necessary to 
provide the twenty-five per cent, overload capacity, because it 
is not likely that all motors will start at the same time. If, 
however, any one motor has more than half the capacity of 
the whole installation, it is advisable to provide the overload 
capacity. For instance, if two motors, each of 50 amperes 
capacity, are fed over a line of 100 amperes capacity and 
one is started while the other is working at full load, they will 
overload that line twelve and one-half per cent. 

For mains supplying many small motors the size should 
be chosen for the total load connected, using the following 
values : 



MOTORS. 8 1 

i io volts 7.5 amperes per horsepower 

220 volts 375 amperes per horsepower 

500 volts 1.65 amperes per horsepower 

Where there are a number of no-volt motors installed on 
the Edison 3-wire system, providing the load is evenly balanced 
between the two sides, the mains may be figured as though 
the motors were operating at 220 volts. The reason for this 
will be easily seen when it is remembered that two no-volt 
motors operating in series on 220 volts (as they do on the 
Edison 3-wire system) take only one-half the current they 
would if operated on a straight 2-wire no-volt system. 

c. Each motor and resistance box must be protected by a 
cut-out and controlled by a switch (see No. 19a), said 
switch plainly indicating whether "on" or "off" (except as pro- 
vided for electric cranes, see No. 43 c). Small motors may 
be grouped under the protection of a single set of fuses, pro- 
vided the rated capacity of the fuses does not exceed 6 
amperes. With motors of one-fourth horse power or less, on 
circuits where the voltage does not exceed 300, single pole 
switches may be used as allowed in No. 24 c. The switch and 
rheostat must be located within sight of the motor, except in 
cases where special permission to locate them elsewhere is 
given, in writing, by the Inspection Department having juris- 
diction. 

Where the circuit-breaking device on the motor-starting 
rheostat disconnects all wires of the circuit, the switch called 
for in this section may be omitted. 

Overload-release devices on motor-starting rheostats will 
not be considered to take the place of the cut-out required by 
this section if they are inoperative during the starting of the 
motor. 

An automatic circuit-breaker disconnecting all wires of the 
circuit may, however, serve as both switch and cut-out. 

Every motor and starting box must be protected by a cut- 
out and controlled by a switch except in the case of groups of 
motors used on electric cranes where only one main switch is 
required and switches need not be placed on the separate 



82 MODERN ELECTRICAL CONSTRUCTION. 

motors. The switch and cutout must be so located that current 
must first pass through them before passing through the start- 
ing box or the motor. For the larger size motors a cutout 
must be provided for each motor, but the smaller motors, such 
as those of nominal i/6th and i/8th horse-power, may be 
grouped on one circuit provided the rated capacity of the fuses 
protecting this circuit do not exceed 6 amperes. 

Small motors of the horse-power mentioned vary greatly 
in the current required to operate them and the horse-power 
ratings are generally of no value in determining the num- 
ber to be allowed on a circuit. The particular conditions ex- 
isting in each case must be taken into consideration and where 
a number of motors are to be switched on at one time the 
starting currents must be provided for. With alternating cur- 
rent motors of small horse-power ratings heavy starting cur- 
rents are frequently required and motors of i/8th horse-power 
rating will often blow six ampere fuses. Obviously motors 
of this kind must each be provided with separate circuits. 

Every motor, whether large or small, must be controlled 
by a switch which will indicate whether the current is on or 
off. A motor may from overload or other causes fail to start 
and if a snap switch is used which does not indicate whether 
the current is on or off it would be easily possible to leave the 
motor with the current turned on. 

As a general rule fused knife switches are used for the 
larger motors, while with the smaller motors cut-out blocks 
and indicating snap switches are often used. If the motor 
is of i /4th horse-power or less, and operated on a circuit 
where the voltage does not exceed 300, a single-pole switch 
may be used. For all motors over i/4th horse-power, and for 
all motors operated on voltages over 300, except in the case of 
street railway circuits, double-pole switches must be used. The 
reason for locating the switch and starting box within sight of 
the motor is that, should any trouble occur when the motor is 



MOTORS. 



83 



being started, such as short circuit or overload, it will be imme- 
diately noticed and the current shut off. It is also possible 
that where the motor and switch are not within sight of each 
other some person might be working on the motor at the time 
it was turned on. Figure 42 shows a complete direct current 
motor installation as usually arranged. 

If the conditions are such that it is necessary to locate the 
motor out of sight of the switch and starting box, the motor 




Figure 42. 



should be located in a safe place away from combustible ma- 
terial. It may also be advisable to provide some means for de- 
termining at the point of control whether or not the motor is 
starting. A switch arranged at the motor to cut off the current 
while any one is working on it will also avoid possible acci- 
dents from that source. A special permit should bet obtained 
from the inspection department having jurisdiction in order 
that the exact conditions may be noted. 



84 MODERN ELECTRICAL CONSTRUCTION. 

d. Rheostats must be so installed as to comply with all 
the requirements of No. 4. Auto starters must comply with 
requirements of No. 4 c. 

Auto starters, unless equipped with tight casings enclos- 
ing all current-carrying parts, in all wet, dusty or linty places, 
must be enclosed in dust-tight, fireproof cabinets. Where there 
is any liability of short circuits across their exposed live parts 
being caused by accidental contacts, a railing must be erected 
around them. 

A starting box is a device for limiting the surrent strength 
during the starting of the motor by inserting a resistance in 
series with the armature. The ohmic resistance of the arma- 
ture of a shunt or compound wound motor is ordinarily very 
small. When such a motor is at rest and the current thrown 
directly on, the full voltage is thrown across the small resis - 
ance of the armature. Consider for a moment the case of a 
1 horsepower no volt motor having an armature resistance of 
say 2 ohms, and taking, when running normally, 8 amperes. 
Suppose the current were thrown on without the use of a 
starting box. According to Ohm's law the current through 
the armature would be 110/2=55 amperes. The results, were 
55 amperes sent through the armature, can easily be imagined. 
Now, suppose a resistance of 8 ohms were inserted in series 
with the armature when starting. In this case 110/10=11 
amperes only would have to pass through the armature, and 
this the armature can easily stand. As the motor begins to 
revolve a counter electro-motive force is generated which op- 
poses the inrush of current. This counter electro-motive force 
increases until the motor reaches full speed and takes its nor- 
mal current. 

In the example given above at the first step of the start- 
ing box there will be a current' of n amperes flowing through 
a resistance of 8 ohms and the power consumed will be 
equal to I 2 R, or 968 watts, which are lost in heat produced 
in the resistance wire. As this amounts to more than one 



MOTORS. 



85 



horsepower thrown off in heat the advisability of mount- 
ing the rheostat away from combustible material and of prop- 
erly ventilating it can readily be seen. 

Figure 43 shows an illustration of an automatic starting 
box, and a diagram of the connections to a motor circuit. It 
will be seen that the resistance coils are in series with the 
armature circuit. As the arm A is moved to the right, resist- 




— WWVWH 



o 



Figure 43. 



ance is gradually cut out of the armature circuit until the 
arm reaches the last point, where it is automatically held in. 
position by means of the small magnet M, which is connected 
in series with the field circuit. By tracing out the circuits it 
will be found that the field connection is made on the first 
point of the rheostat, so that when the arm A is in the "off" 
position there is no current passing through the field coils. 
It will also be noticed that the last contact upon which the 
arm rests when "off" is dead. 



86 



MODERN ELECTRICAL CONSTRUCTION. 



If the supply current for any reason fails, current will cease 
to flow around the coils of the magnet M and it will become 
demagnetized, thus allowing the arm A to fly back to the "off" 
position. This prevents the main current being momentarily 
shut off and then thrown on when all the resistance is out of 
the armature circuit. This device is known as "no-voltage" 
release. 

Another device known as the "overload" release is shown 
in Figure 44, with a diagram of the connections. The wind- 
ing of the magnet Mi carries the main current. When the 




laaaaa- 

1 — vwwws 



o 



Figure 44. 



current exceeds a certain amount (which can be regulated 
by an adjusting screw the armature below the magnet will be 
attracted, thus short circuiting the coil M and allowing the 
arm to fly back and shut off the current to the motor. This 
device cannot be considered to take the place of the regular 
cut-outs, as it is not operative during the starting of the 



MOTORS. 



87 



motor. It can only operate after the arm A is held in posi- 
tion by the magnet M. 

Starting boxes are made in different designs to meet the 
requirements of the various classes of work on which they 




Figure 45. 



are used. Figure 45 shows a large automatic starting box 
where the resistance is cut out by the action of the solenoid 
S, which draws up the movable arm. When solenoids are 
used for this purpose it is often advisable to arrange the 
connections so that when the movable arm has been raised 
to the highest and last point a resistance will be inserted 
in series with the solenoid to cut down the current and reduce 
the heating in the coil, as less current is required to hold 
the arm in place than to move it over the contacts. Incan- 



88 MODERN ELECTRICAL CONSTRUCTION. 

descent lamps are often used for this purpose and must be in- 
stalled as in 4, Class A. 

A speed controller differs from a starting box mainly in 
the size of wire used as resistance. The resistance coils of a 
starting box are wound with comparatively small-wire and 
connected in circuit for a short time only, generally from ten 




Figure 46. 

to twenty seconds, while in a speed controller the wire must 
be of sufficient size to carry the current as long as the motor 
is running. Another difference between the starting box and 
speed controller is the automatic coil (Fig. 43) M, which in 
the speed controller is arranged to hold the arm A in any 
position in which it may be placed. This is accomplished 'in 
some types of speed controllers by a lever attached to an 



MOTORS. 89 

armature, which is attracted by the magnet M, the other end 
of the lever fitting into a series of indentations on lower part 
of movable arm. 

While the underwriters' rules do not require a speed con- 
troller to be automatic, still it is good practice to make them 
so, as the same principles apply to the starting of a motor 
with a speed controller as with a starting box. 

Figure 46 shows a circuit breaker which is operative dur- 
ing the starting of the motor, and can be used to take the 
place of the switch required. Circuit breakers should be fre- 
quently operated to assure that they are in working condition. 
This is especially necessary in wet or damp places where the 
mechanism is likely to become corroded and under such con- 
ditions it is sometimes advisable to use the circuit breaker for 
the usual operation of the apparatus in place of the switch. 
Overload devices on starting rheostats are also subject to 
corrosion in damp places and they should be frequently op- 
erated. 

As the arm of a starting box or speed controller is moved 
from one contact to another, more or less sparking results, 
and, as has already been stated, considerable heat is developed 
in the coils. A rheostat should never be located in a room 
where either inflammable gases or dust exist. If a starting box 
is to be located in a room where considerable dirt is apt to 
gather, or if the room is unusually damp, the starting box 
should be mounted in a dust-tight fireproof box, which should 
be kept closed at all times, except when starting the motor. 
If the enclosing box is rather large, sufficient ventilation of 
the coils will be obtained while the motor is being started 
and the door open. A speed controller should never be 
mounted in an enclosure unless the same is arranged to give 
a thorough ventilation to the outside air, as heat is constantly 
being generated in the coils of the rheostat, and this heat must 
be dissipated. A speed controller should never be located 



90 



MODERN ELECTRICAL CONSTRUCTION. 



where dust or lint is apt to gather on it. If it is necessary to 
use one on a motor located in such a place, it should be 
mounted outside the room. 

In metal working establishments or in any place where 
there is a liability of the contacts on the switches or the start- 




Figure 47. 



ing boxes being short-circuited, they should be enclosed or 
suitably protected. 

Rheostats used in wet or damp places are more or less 
liable to corrosion of both the resistance elements and the 
sliding contact surfaces. A rheostat which has proven itself 
especially applicable in such places is shown in Figure 47. This 
rheostat is manufactured by the Allen-Bradley Co. and consists 
of a number of prepared graphite discs piled in a column and 



MOTORS. 91 

placed under compression by the movement of the lever arm 
of the starter. An imperfect contact between the discs when 
"under slight compression increases the resistance at starting. 
As the discs are compressed the contact between adjacent discs 
become better and the resistance is gradually decreased. These 





Figure 48. 

starters are not affected by moisture or acid fumes. Figure 48 
shows one of the resistance elements of this type starter. 

With the ordinary type of rheostat having wire wound re- 
sistance tubes and sliding contacts if used in wet or damp 
places it is often advisable to place them in waterproof en- 
closures with an incandescent lamp arranged for constant burn- 
ing. The heat of the lamp will keep the rheostat dry and 
greatly lessen the corrosion and liability of trouble. 



92 MODERN ELECTRICAL CONSTRUCTION. 

Auto starters answer the same purpose with alternating 
current motors that starting boxes do with direct current mo- 
tors. The method whereby this is accomplished is, however, 
somewhat different, the ohmic resistance inserted in the arma- 
ture circuit in the case of direct current motors being re- 
placed by an auto transformer. 

An induction motor when at rest is, in so far as its start- 
ing current is concerned, very similar to the direct current 
motor. When current is turned on the motor is at rest and 
the whole device is simply a transformer with the secondary 
short circuited. 

There are a number of auto starters in use at the present 
time which consist of a double throw ©witch with five switch 
blades which connect the motor to taps taken from an auto 
transformer for starting. This gives a reduced voltage and 
keeps down the starting current. When the motor is up to 
speed the switch is thrown oyer and connects the motor direct 
to the line with full line voltage. 

This type of auto starter is often misused and where left 
to the care of an ordinary workman it is more likely to be 
abused than rightly used. It is open to the following objec- 
tions: 

The operator may not use the starting position at all with 
the result that the main line is greatly overfused to allow the 
enormous starting current. 

He may not allow time enough on the starting position for 
the motor to come up to proper speed. 

He may start the motor a little, open the circuit for an in- 
stant, close again, as many do thinking they are saving the 
motor. 

He may start on the running position and leave the motor 
running on this position. 

He may reverse the proper order and start on the running 
position and then move the switch to the starting position. 



MOTORS. 



93 



To obviate these difficulties the rules now demand that auto 
starters be designed so that they cannot be started except on 
the starting position and cannot be placed on the running posi- 
tion until they have passed through the starting position. See 
construction rules No. 79. 

A starter designed to comply with these rules and to pro- 




Figure 49. 

vide for both overload and cessation of current is shown in 
Figure 49. 

The two rows of contact points A and C are stationary the 
contact piece B being operated by a starting lever. The device 
is so constructed that contact must be made on the starting 
position before it can be thrown on the running position. 
When connection is established between the contacts on B and 
C the motor circuit is placed in connection with the taps taken 



94 



MODERN ELECTRICAL CONSTRUCTION. 



off the auto transformer and the motor starts on the reduced 
voltage and protected only by the fuses in the main line which 
must be of sufficient capacity to allow for the starting current. 
When the motor has come up to speed the contacts B are 
moved to the upper position where the motor is connected di- 
rectly to the line through the two overload coils M M. The 
starting arm is held in position by means of the no voltage 
coil N. If the current fails, or if, on account of overload, the 



"W~ 



WW* 






Figure 50. 



no voltage coil circuit through N is broken the arm returns 
at the off position cutting the motor dead. 

There is very little heat developed in the coils of an auto 
starter and they may, if of approved type, be mounted directly 
on wood work with no added protection. 

e. Must not be run in series-multiple or multiple-series, 
except on constant-potential systems, and then only by special 
permission of the Inspection Department having jurisdiction. 

Figure 50 shows a series-multiple, and Figure 51 a multiple- 
series system of wiring. 

/. Must be covered with a waterproof cover when not in 
use, and, if deemed necessary by the Inspection Department 
having jurisdiction, must be enclosed in an approved case. 

Such enclosures must be readily accessible, dust proof and 
sufficiently ventilated to prevent an excessive rise of tempera- 



MOTORS. 95 

hire. Where practicable the sides should be made largely of 
glass, so that the motor may be always plainly visible. 

The use of enclosed type motor is recommended in dusty 
places, being preferable to wooden boxing. 

Under certain conditions it is found necessary to enclose 
motors in dust-tight enclosures. The practice of building a 





Figure 51. 

small box which fits entirely around the motor, enclosing the 
pulley and provided with slots through which the belt passes, 
is very unsatisfactory. While this construction prevents con- 
siderable dust from settling on and around the motor, still 
a great deal will be carried in by the belt. If the box is so 
made that it fits tightly around the shaft between the pulley 
and the motor frame and is otherwise well constructed, most 
of the dust and dirt can be kept out. As the efficient work- 
ing of the motor requires that it be kept as cool as possible, 
the box should afford sufficient ventilation. This may be ob- 
tained by making the box somewhat larger than the motor, 
thus allowing the heat to radiate from the sides, or the box 
should be ventilated to the outside air. 

A number of motors are so constructed that, by means of 
hand plates, they can be entirely enclosed. When they are so 
enclosed their efficiency and capacities are somewhat reduced, 
but cases are sometimes found where the conditions require 
motors of this kind to be used. 

In places where there is considerable dust flying about in 



96 MODERN ELECTRICAL CONSTRUCTION. 

the air, and where the dust is not readily combustible, a fine 
gauze can be used to close the hand holes. This gauze will 
allow ventilation, but will prevent the dirt from gathering 
inside the motor. The alternating induction motors, which are 
operated without brushes or collector rings, can be used in 
almost any location, as there is no sparking. 

In large woodworking establishments there is generally 
compressed air available and arrangements should be pro- 
vided by which the motors may be blown out regularly. Hand 
bellows are used for this purpose but the pressure is not suf- 
ficient for good work. 

g. Must, when combined with ceiling fans, be hung from 
insulated hooks, or else there must be an insulator interposed 
between the motor and its support. 

Ceiling fans are generally provided with an insulating knob 
on which the fan hangs. If this is not provided, a simple 
knob break can be used, or the fan can be suspended from a 
hook screwed into a hardwood block, provided the hook does 
not pass through the block into the plaster, the block being 
separately supported from the ceiling. 

h. Must each be provided with a name-plate, giving the 
maker's name, the capacity in volts and amperes, and the nor- 
mal speed in revolutions per minute. 

All varying (or variable) speed alternating current motors 
except those used for railway service must be marked with 
the maximum current which they can safely carry for 30 
minutes, starting cold. 

i. Terminal blocks when used on motors must be made 
of approved non-combustible, non-absorptive, insulating ma- 
terial such as slate, marble or porcelain. 

;. Adjustable speed motors, unless of special and appro- 
priate design, if controlled by means of field regulation, must 
be so arranged and connected that they cannot be started un- 
der weakened field. 

The speed of a motor may be changed either by inserting 



MOTORS. 



97 



resistance in series with the armature, thereby cutting down 
the voltage at the armature terminals ; or by decreasing the 
field current through the addition of resistance in series with 
the shunt field winding. By this latter method the lines of 
force passing through the armature gap are considerably de- 
creased and the armature must therefore revolve at a greater 
speed to develop the proper counter electro-motive force. 
When a motor is started under a weakened field, the starting 
torque being reduced, the armature is slow in coming up to 




Figure 52. 



speed. This prevents the rapid rise of counter E. M. F. which 
takes place in the ordinary motor and consequently the heavy 
rush of current through the armature is more likely to con- 
tinue and burn out the armature. 

Unless motors are so designed that they do not require 
this excessive current when starting under a weakened field, 
the field rheostat, if separate from the starting rheostat, must 
be provided with a no-voltage release, such as is described in 
Figure 43. When the field rheostat is combined with the start- 



08 MODERN ELECTRICAL CONSTRUCTION. 

ing rheostat the apparatus should be so constructed that the 
motor cannot be started under a weakened field. Figure 52 
shows a starting rheostat of this kind, the last four con- 
tacts at the right being connected to the shunt field resistance. 
Moving the rheostat arm to the right cuts this resistance in 
series with the shunt field. 

9. Railway Power Plants. 

a. Each feed wire before it leaves the power plant must 
be protected by an approved automatic circuit-breaker or 
other device, which will immediately cut off the current in 
case of an accidental ground. This device must be mounted 
on a fire-proof base and in full view and reach of the at- 
tendant. 

10. Storage or Primary Batteries. 

a. When current for light or power is taken from primary 
or secondary batteries, the same general regulations must be 
observed as apply to similar apparatus fed from generators 
developing the same difference of potential. 

b. Storage battery rooms must be thoroughly ventilated. 

c. Special attention is directed to the rules for wiring in 
rooms where acid fumes exist (see No. 26 i and /). 

d. All secondary batteries must be mounted on non-ab- 
sorptive, non-combustible insulators, such as glass or thor- 
oughly vitrified and glazed porcelain. 

e. The use of any metal liable to corrosion must be 
avoided in cell connections of secondary batteries. 

Rubber-covered wire run on glass knobs should be used 
for wiring storage battery rooms. The knobs should be of 
such size as to keep the wire at least one inch from the sur- 
face wired over, and they should be separated 2V2 inches 
for voltage up to 300 and 4 inches for voltage over 300. 
Waterproof sockets hung from stranded rubber covered wire 
and properly supported independently of the joints should be 
used ; these lights to be controlled by a switch placed outside 
of battery room. All joints after being properly soldered and 



TRANSFORMERS. 99 

taped with both rubber and friction tape should be painted 
with some good insulating compound. This tends to keep 
all acid fumes away from the wire. 

Acid fumes are not only liable to bring about a fire hazard, 
but are also irritating to employes. Thorough ventilation is 
therefore very important. It is also important that a motor, 
if one is used on the ventilating fan, be kept outside the 
battery room as the arc produced on starting the motor is 
liable to cause an explosion from the accumulated gases. 

11. Transformers. 

(See also Nos. 14, 15, 36 and 45. For construction rules, 

see No. 81.) 

a. In central or sub-stations the transformers must be 
so placed that smoke from the burning out of the coils or the 
boiling over of the oil (where oil filled cases are used) could 
do no harm. 

b. In central or sub-stations casing of all transformers 
must be permanently and effectively grounded. 

Transformers used exclusively to supply current to switch- 
board instruments need not be grounded, provided they are 
thoroughly insulated. 



NOTICE.— DO NOT FAIL TO SEE WHETHER ANY 
RULE OR ORDINANCE OF YOUR CITY CONFLICTS 
WITH THESE RULES. 

Class B. 
OUTSIDE WORK. 

(Light, Power and Heat. For Signaling Systems, see Class E.) 

All Systems and Voltages. 

12. Wires. 

a. Line wires must have an approved weatherproof or 
rubber insulating covering. That portion of the service wires 
between the main cut-out and switch and the first support 
from the cut-out or switch on outside of the building must 
have an approved rubber insulating covering, but from the 
above mentioned support to the line, except when run in con- 
duit, may have an approved weatherproof insulating covering, 
if kept free from awnings, swinging signs, shutters, etc. 

By service wires are meant those wires which enter the 
building. It is customary to run the rubber-covered wire 
from the service switch and cut-out inside of building through 
the outer walls, and to leave but a few feet of wire to which 
the line wires can later be spliced. This is illustrated in 
Figure 55, which shows how wires are run from pole to 
building. 

b. Must be so placed that moisture cannot form a cross 
connection bewteen them, and except when run in conduit, 
not less than a foot apart, and not in contact with any sub- 
stance other than their insulating supports. Wooden blocks 
to which insulators are attached must be covered over their 
entire surface with at least two coats of waterproof paint. 



OUTSIDE WORK. IOI 

For conduit work, wires must be placed so as to conform 
to rules for unlined conduit except that conduit system must 
be waterproof. 

c. Must be at least seven feet above the highest point of 
flat roofs, and at least one foot above the ridge of pitched 
roofs over which they pass or to which they are attached and 
roof structures must be substantially constructed. 

For conduit work exposed to the weather all joints should 
be leaded. Marine type boxes should be used, or in lieu of 
these, special waterproof boxes. The marine type box is pro- 
vided with a threaded inlet into which the pipe can be screwed 
and is also provided with a gasketed cover. Special boxes 
follow this same design and are arranged to be made abso- 
lutely watertight. The ordinary conduit construction with 
locknuts and bushings should never be used for outside work. 

It is well to avoid fastening wires perpendicular above one 
another, as in winter icicles may form which extend from the 
top to the lower wire, and the moisture on these will often 
cause much trouble. The rule requires that wires be 7 feet 
above flat roofs, and roof structures must, therefore, be made 
high enough to allow for "sag." In moderately long runs 
2 or 3 feet will be sufficient. For long runs, see following 
table, taken from construction rules of Commonwealth Edison 
Company of Chicago : 

The tension on wires should be such that the sag of a 
span of 125 feet will not exceed the amounts shown. 
Temperature, F..10 20 30 40 50 60 70 80 90 
Sag, inches 6 8 8 10 10 12 12 14 14 ■ 

This table will also be useful to consult when running wires 
over housetops to which they are not attached, as it shows 
the variation in "sag" due to different temperatures. Wires 
should be so run that even at the highest temperature they 
will still clear the buildings. Allowance should also be made 
for the gradual elongation of the wire to its own weight, giv- 



102 



MODERN ELECTRICAL CONSTRUCTION. 



ing way of supports or sleet that may at times weigh it 
down. 

d. Must, where exposed to the weather, be provided with 
petticoat insulators of glass or porcelain ; porcelain knobs or 
cleats and rubber hooks will not be approved. Wires on the 
exterior walls of buildings must be supported at least every 
fifteen feet, the distance between supports to be shortened 
if wires are liable to be disturbed. 

Where not exposed to the weather, low potential wires 
may be supported on glass or porcelain knobs which will 
separate the wires at least one inch from the surface wired 
over, supports to be placed at least every four and one-half 
feet. 

In Figure 53 single and double petticoat insulators are 
shown. It is very often convenient to fasten such insulators 





'WWVVWVv 

Figure 53. 



m £3 




upside down or horizontally, but this should never be done, 
as they will then fill with water or dirt and their insulating 
qualities be destroyed. 

e. Must be so spliced or joined as to be both mechani- 
cally and electrically secure without solder. The joints must 
then be soldered, to insure preservation, and covered with an 
insulation equal to that on the conductors. 

All joints must be soldered, unless made with some form 
of approved splicing device. 

Figure 54 shows a splicing device used for large cables 
on outside lines. 



OUTSIDE WORK. 103 

/. Must, where they enter buildings, have drip loops 
outside, and the holes through which the conductors pass 
must be bushed with non-combustible, non-absorptive, in- 
sulating tubes slanting upward toward the inside. 

' For low-potential systems the service wires may be 
brought into buildings through a single iron conduit. The 
conduit to be equipped with an approved service-head. The 
inner end must extend to the service cut-out, and if a cabinet 
is required by the Code must properly enter the cabinet. 

The manner of bringing in overhead services is shown in 
Figure 55. 

Although the rule does not specify the height at which 
service wires must be brought out it is good practice to bring 




Figure 54. 

them out at the level of the ceiling of the second floor. In 
almost all cases telephone wires are run on the lower cross 
arms of poles and if the service wir^s are brought out as sug- 
gested little trouble will be encountered from interference with 
these wires. 

g. Electric light and power wires must not be placed on 
the same cross-arm with telegraph, telephone or similar wires, 



104 



MODERN ELECTRICAL CONSTRUCTION. 



and when placed on the same pole with such wires the dis- 
tance between the two inside pins of each cross-arm must not 
be less than twenty-six inches. 

h. The metallic sheaths to cables must be permanently 
and effectively connected to "earth." 

Telephone or telegraph wires are sometimes placed above 
power wires and it then becomes necessary for a lineman to 
pass through the lower wires, which are generally of a high 
potential, to get to the upper ones. Great care is then nec- 




Seroice 
Si tttcV> 



Figure 55. 



cessary both in passing through the wires and in working on 
the upper wires. The better practice is to place the power 
(or lighting) wires on the upper cross arms. Being stronger, 
they are less liable to break and fall on the lower wires, and 
it is then unnecessary for the lineman working on the tele- 
phone or telegraph wires to come near the higher potential 
wires. 

Poles should not be set more than 125 feet apart; 100 or 
no feet is good practice. For small wires poles with 6-inch 
tops are often used, but for heavier wires 7-inch tops are 



OUTSIDE WORK. 105 

advisable. The tops of pole should be pointed, so as to shed 
water, and the whole pole be well painted. Steps should be 
placed so that the distance between any two steps on the same 
side is not over 36 inches; these steps should all be the same 
distance apart, and should not extend nearer than 8 feet to 
the ground. All "gains" cut into poles should be painted be- 
fore cross-arms are placed in them. Such places are more 
iikely to hold moisture and rot than exposed parts. Where- 
ever feed wires end or sharp angles occur, double cross-arms 
should be used, fastened on opposite sides of pole and bolted 
together. 

All bolts, lag screws, etc., should be galvanized. Poles 
should be set at least as far into the ground as shown in 
the following table : 

Length of poles. Depth in ground. 

35 feet 5^ feet 

40 feet 6 feet 

45 feet 6 feet 

50 feet 6Y 2 feet 

55 feet 7 feet. 

60 feet 8 feet 

The holes should be large enough to admit of thorough 
tamping on all sides of bottom of hole. If the tamping at 
bottom of hole is not well done, the pole will always be shaky, 
no matter how much tamping may be done at the top. If 
the ground is soft, the pole may be set in cement, or short 
pieces of planking fastened to it at right angles underground. 
At the end of line or where sharp bends occur, strong gal- 
vanized guy cables fastened to poles six or eight feet long, 
buried underground should be used. 

Trolley Wires. 

i. Must not be smaller than No. o B. & S. gage copper 
or No. 4 B. & S. gage silicon bronze, and must readily stand 
the strain put upon them when in use. 



joo 



MOM.KN II I < I RI( \l. < iiNS'1 Kl( I ION, 



/. Must have a double insulation from the ground. In 
wooden pole construction the pole will be considered as one 

insula! ion. 

k, Mu i be capable of being disconnected at the power 
plant, or of being divided into sections, so thai in case of fire 
on the railway route, the current may be shut off from the 
particular section and nol interfere with the work of the fire- 
men, I his i ule als< i applies i<> feedei s. 

/. Musi be safely protected against accidental contact 

where Crossed l>y other conductors. 

Where guard wires are Used they must be insulated from 

the ground and electrically disconnected in sections of not 

more than 30O feet in Length. 

Ground Return Wires. 

m. For the diminution of electrolytic corrosion of under- 
ground metal work, ground return wires must be so arranged 
that the difference of potential between the grounded dynamo 
terminal and any point on the return circuit will not exceed 
twenty five volts. 

It is suggested that the positive pole of the dynamo be 

connected to the trolley line, and that whenever pipes or other 
Underground metal work are found to he electrically positive 

to the rails or surrounding earth, that they he connected hy 
conductors arranged so as to prevent as far as possible cm 

rent How from the pipes into tin- ground. 

Where trolley wires enter buildings an arrangement such 

as shown in Figure 56 is often used. The car in passing 




Figure 56. 



forces the arm at the right upward energizing the trolley 
wiic inside the building. When the c;ir leaves the building the 



OUTSIDE WORK. 107 

left arm is forced up and the trolley wire inside the building 
mncted, 
In cases where the trolley wire passes through the build- 
ing arrangements maj be made so thai the same action is ob- 
tained through the medium of electro magnets energized as 
the car entei and leaves the building. 

13. Constant-Potential Pole Lines, Over 5,000 Volts. 

(Overhead lines of this class miles, properly arranged 
may increase the fire loss from the following causes: 

Accidental crosses between such lines and low-potential 
lines may allow the high voltage current to enter buildii 
over a large ection of adjoining country. Moreover, such 
high voltage hues, if carried dose to buildings, hamper the 
work of firemen in ca e of fire in the building. 'I he object 
of these rules is so to direcl tin's class of construction that 
no increase in Tire hazard will result, while at the same time 
care ha been taken to avoid restrictions which would unrea- 
onably impede progress in electrical development. 

It is fully under tood that it is impossible to frame rules 
which will cover all conceivable cases that may arise in con- 
struction work of such an extended and varied nature, and 
it i advi ed that the In pection Department having jurisdic- 
tion be freely con ulted as to any modification of the rul< i 
in particular ca e I 

a Every reasonable precaution must be taken in arrang 

route; so as to avoir! exposure to contacts with Other 
electric circuits. On existing lines, where there is a liability 
to contact, the route should be changed by mutual agree- 
ment between the parties in interest wherever possible. 

h. Such lines should not approach other pole linet nearer 

than a distance equal to the height of the taller pole line, and 

ii'-Ji lines should not be on the same pples with oiher wires, 

epl that signaling wires used by the company operating 

the high pre ure system, and which do not enter property 



108 MODERN ELECTRICAL CONSTRUCTION. 

other than that owned or occupied by such company, may be 
carried over the same poles. 

c. Where such lines must necessarily be carried nearer 
to other pole lines than is specified in Section b above, or 
where they must necessarily be carried on the same poles with 
other wires, extra precautions to reduce the liability of a 
breakdown to a minimum must be taken, such as the use of 
wires of ample mechanical strength, widely spaced cross- 
arms, short spans, double or extra heavy cross-arms, extra 
heavy pins, insulators, and poles thoroughly supported. If 
carried on the same poles with other wires, the high-pressure 
wires must be carried at least three feet above the other wires. 

d. Where such lines cross other lines, the poles of both 
lines must be of heavy and substantial construction. 

Wherever it is feasible, end-insulator guards should be 
placed on the cross-arms of the upper line. If the high-pres- 
sure wires cross below the other lines, the wires of the upper 
line should be dead-ended at each end of the span to double- 
grooved, or to standard transposition insulators, and the line 
completed by loops. 

One of the following forms of construction must then be 
adopted : 

I. The height and length of the cross-over span may 
be made such that the shortest distance between 
the lower cross-arms of the upper line and any 
wire of the lower line will be greater than the 
length of the cross-over span, so that a wire break- 
ing near one of the upper pins would not be long 
enough to reach any wire of the lower line. The 
high-pressure wires should preferably be above the 
other wires. 

By reference to Fig. 57 it will be seen that the first plan 
of making cross-over is not very practical. In the lower left 
hand corner the vertical lines drawn alongside of the pole 
show the rate at which poles must be lengthened to comply 
with the rules when they are some distance from the pole to 
be crossed. 



OUTSIDE WORK. 



109 



If a line is to be crossed in this manner, economy and also 
good construction require that the poles be set close to the 
line to be crossed as shown at the right of the figure. The 
poles here are about twice the length of the cross-arm apart. 
The wires between the two poles cannot touch the lower wires 




Figure 57. 



and the expense of the cross-over is only the setting of one 
pole and its cross-arms, etc. With the poles set as close as 
this there remains, however, the possibility of a wire in one 
of the adjacent spans breaking and, if strongly whipped about 
by the wind, being lashed against the lower wires. Guard 



no 



MODERN ELECTRICAL CONSTRUCTION. 



wires can in a measure prevent such a wire coming in contact 
with the lower wire, but it is conceivable that the wire in ques- 
tion be broken off at such a distance from the pole that it will 
swing over and lodge on top of the lower wires. If the cross- 
over poles are to be set farther apart to lessen this danger, 
they must be increased two feet in height for every foot they 
are moved to one side. 

Figure 58 is a suggestion towards making crosses on a 
joint pole. It is simply a trough-like screen built around 



??9*9 


ifl *???? 




m TT i 


Mill 


fl MM 







!3 



Figure 58. 



the lower wires and set so that it must catch the upper wires 
when they break and confine them so that the wind cannot 
whip them out. 

A cross-over made on a joint pole in some such manner 
as this is probably the most satisfactory. Wires are abso- 
lutely prevented from coming together, and such a pole be- 
ing braced by the wires in two ways would seem to be quite 
safe. When wires cross at rather an acute angle the screen 
mentioned stretched from pole to pole under the upper wires 
is probably the best safeguard. 



OUTSIDE WORK. Ill 

2. A joint pole may be erected at the crossing point, 

high-pressure wires being supported on this pole 
at least three feet above the other wires. Mechan- 
ical guards or supports must then be provided, so 
that in case of the breaking of any upper wire it 
will be impossible for it to come into contact with 
any of the lower wires. 

Such liability of contact may be prevented by the use 
of suspension wires, similar to those employed for sus- 
pending aerial telephone cables, which will prevent the 
high-pressure wires from falling in case they break. 
The suspension wires should be supported on high po- 
tential insulators, should have ample mechanical 
strength, and should be carried over the high-pressure 
wires for one span on each side of the joint pole, or 
where suspension wires are not desired guard wires may 
be carried above and below the lower wires for one span 
on each side of the joint pole, and so spread that a fall- 
ing high-pressure wire would be held out of contact with 
the lower wires. 

Such guard wires should be supported on high-poten- 
tial insulators or should be grounded. When grounded, 
they must be of such size, and so connected and earthed, 
that they can surely carry to ground any current which 
may be delivered by any of the high-pressure wires. Fur- 
ther, the construction must be such that the guard wires 
will not be destroyed by any arcing at the point of con- 
tact likely to occur under the conditions existing. 

3. Whenever neither of the above methods is feasible 

a screen of wires should be interposed between 
the lines at the cross-over. This screen should be 
supported on high tension insulators or grounded 
and should be of such construction and strength 
as to prevent the upper wires from coming into 
contact with the lower ones. 

If the screen is grounded each wire of the screen must 
be of such size and so connected and earthed that it can 
surely carry to ground any current which may be de- 
livered by any of the high pressure wires. Further, the 
construction must be such that the wires of screen will 
not be destroyed by any arcing at the point of contact 
likely to occur under the conditions existing. 

e. When it is necessary to carry such lines near buildings, 
they must be at such height and distance from the building 
as not to interfere with firemen in event of fire ; therefore, if 
within 25 feet of a building, they must be carried at a height 
not less than that of the front cornice, and the height must 



112 



MODERN ELECTRICAL CONSTRUCTION. 



be greater than that of the cornice, as the wires come nearer 
to the building, in accordance with the following table : — 
Distance of wire Elevation of wire 

from building. above cornice of building. 

Feet. Feet. 

25 

20 2 

15 4 

10 6 

5 8 

2% 9 

It is evident that where the roof of the building continues nearly 
in line with the walls, as in mansard roofs, the height and dis- 



5-J 




Figure 59. 



tance of the line must be reckoned from some part of the roof in- 
stead of from the cornice. 



OUTSIDE WORK. 1 13 

A graphic illustration of the rule concerning the plac- 
ing of poles near buildings is given in Figure 59. The upper 
group of figures and insulators shows the distance from the 
building and the corresponding height above high point of 
roof required with mansard roofs. Distance being measured 
from the roof. The lower groups show measurements taken 
from cornice line as will be proper with ordinary flat roofed 
buildings. 

14. Transformers. 

(See also Nos. 11, 15, 36 and 45. For construction rules, see 

No. 81.) 

Where transformers are to be connected to high -voltage circuits, 
it is neecssary in many cases, for best protection to life and prop- 
erty, that the secondary system be permanently grounded, and pro- 
vision should be made for it when the transformers are built. 

a. Must not be placed inside of any building, excepting 
central stations and sub-stations (except as provided in No. 
36), unless by special permission of the Inspection Depart- 
ment having jurisdiction. 

b. Must not be attached to the outside walls of buildings, 
unless separated therefrom by substantial supports. 

Must not be attached to frame buildings when any other 
location is practicable. 

As a rule transformers are fastened to buildings on hori- 
zontal bars of wood. This method is as satisfactory as any if 
the wood itself is securely enough fastened to the wall. The 
wooden supports of the transformer should be fastened to the 
wall either by suitable expansion bolts or better still by bolts 
pa.ssing entirely through the wall. In fastening transformers 
to poorly constructed walls where permission to go through 
the wall cannot be obtained, some advantage can be gained 
by supporting the transformer supports set vertically as shown 
in Figure 60. It must be borne in mind that there is not only 
a downward strain on the supports but also an outward 



H4 



MODERN ELECTRICAL CONSTRUCTION. 



tipping strain. Almost any wall will stand the downward 
strain but in a loosely constructed wall there may not be a 
good hold for the bolts and a heavy transformer may tear them 
out as indicated. If the transformer is supported as shown 
the supports may be distributed over a much larger wall area 
and a much greater leverage obtained against tipping strain 
than would be possible with horizontally arranged timbers. It 




Figure 60. 



is always better practice when possible to keep transformers 
off of buildings and mount them on poles. 

The alternating current transformer consists of an iron 
core upon which wires of two distinct electrical circuits are 
wound. One of these is known as the primary circuit, and in 
it the high pressure currents coming direct from the dynamo 
circulate. The other is known as the secondary circuit, and 
in it the low pressure currents used inside of building circu- 
late. These two circuits are wound generally one over the 
other, and are very close together. The pressure used in the 



OUTSIDE WORK. 115 

primary coil is from 1,000 to 5,000 volts, while in the secondary- 
it is reduced usually to no or 220. 

It quite frequently happens that the insulation between 
the two windings breaks down and thus the high pressure is 
accidentally brought into buildings. Under such circumstances 
should any one touch any live part of the installation while 
touching also grounded parts of the building death would 
very likely result. Also, should there be a weak spot in the 
insulation, it is quite likely the high pressure would pierce it 
at that point with a possible result of a fire. Many deaths 
and fires have been caused in this way. If such lines are con- 
nected to ground the chances for harm are very much les- 
sened, for the current will never take the path of high resist- 
ance through a man's body while a direct path through a low 
resistance wire is open to it. 

It must not be supposed that "grounding" one side of an 
electric light system is not often followed by serious conse- 
quences, for under such circumstances a ground coming on 
any other part of the system will cause a short circuit at 
once. The grounding in these cases is to he looked upon as 
the lesser of two evils rather than as an advantage. 

Grounding the secondary tends to increase the danger 
from fire by increasing the electrical strain on the wires and 
fittings and, further, by increasing the tendency to short cir- 
cuits. In an ungrounded system there is always the insulation 
of both sides of the system between conductors of opposite 
polarity as, for instance, in the case of the wires where cur- 
rent must pass through two insulations before a short cir- 
cuit can occur, it is also necessary for both sides of the sys- 
tem to become grounded before a short circuit can occur. In 
the grounded system the insulation on the grounded wire is 
useless so far as short circuits through the ground are con- 
cerned as current must pass through one insulation only to 
produce a short. 



Il6 MODERN ELECTRICAL CONSTRUCTION. 

On the other hand the danger to life is greatly decreased 
by the grounding of the secondary as has already been ex- 
plained, and the danger from fire is somewhat decreased by 
making it impossible for the high tension current to enter the 
building. As secondary voltages for commercial use vary from 
no to 550 volts it is evident that some limit must be placed 
on the secondary voltage which it shall be permissible to 
ground. Obviously it would be inadvisable to ground a sec- 
ondary having a potential of 550 volts to ground as the danger 
from fire and to life would be greatly increased. The proper 
limiting voltage for grounding has been a subject of much 
discussion. The solution of the question as it effects the 
fire hazard is determined by the number of fires occuring on 
systems with grounded secondaries from short circuits on the 
secondary and the number of fires occurring from crosses be- 
tween the primary and secondaries. The proper voltage is, 
of course, that voltage which will give the minimum number 
of fires. 

The limiting voltage from the life standpoint is likewise 
determined. It is a matter of record that numbers of fatal 
accidents have occurred from contact with both no and 220 
volt circuits, while a contact with a secondary which has be- 
come crossed with the primary nearly always results fatally. 
The Underwriters have set the limiting voltage at 250. (See 
Rule 15 b.) 

With alternating currents, the chances of possible dam- 
age from grounding are less than with direct currents, be- 
cause each transformer with its small group of lamps is a 
system by itself and not affected by grounds on other trans- 
formers. Thus a 5,000 light alternating current installation 
would consist of from 25 to 50 separate systems, each in- 
dependent of defects on the rest, while in a continuous cur- 
tent installation a ground on the most remote branch circuit 



OUTSIDE WORK. 



117 



would, in conjunction with a ground on the opposite side 
of any other part of the system, form a short circuit. 

The benefits of both the grounded and the ungrounded 
secondary system can be obtained by interposing a one to 
one transformer in the secondary circuit. This transformer 
does not alter the voltage but simply insulates the two parts 



/WVs/SAA A AAMAA ^ /VN/NA/VW^ 

-^ 1/SrZZQV. "fc usv. "^zzov. 




^ £30 Y. 

Gib 



ym 



/VW^ /WN/\ /\/\A^v 

^- J.00V. 



1 — ff v l \} y 

— y= 



Figure 61. 

of the secondary circuit. It is frequently used where the sec- 
ondaries are especially liable to grounds as in packing houses 
and breweries. 

Methods of grounding secondary wires of alternating cur- 
rent transformers are shown in Figure 61. 

In connection with 3-wire systems, grounding of the neu- 
tral wire can do little harm, because ordinarily the neutral 



Il8 MODERN ELECTRICAL CONSTRUCTION. 

wire seldom carries much current, and that current is apt to 
vary in direction so that the electrolytic effect will be on the 
whole quite negligible. 

In connection with 3-wire systems, however, it is of the 
greatest importance (as more fully explained further on) that 
the neutral wire remain intact, and it being thoroughly 
grounded at all available outside places will help to keep it so. 

15. Grounding Low-Potential Circuits. 

The grounding of low-potential circuits under the following regu- 
lations is only allowed when such circuits are so arranged that un- 
der normal conditions of service there will be no passage of current 
over the ground wire. 

Direct-Current 3-Wire Systems. 

a. Neutral wire may be grounded, and when grounded 
the following rules must be complied with : — 

1. Must be permanently and effectively grounded at the 

Central Station. The ground connection must in- 
clude all available underground water and gas pipe 
systems. 

2. In underground systems the neutral wire must also 

be grounded at each distributing box through the 
box. 

3. In overhead systems the neutral wire must be 

grounded every 500 feet, as provided in Sections 
c to g. 
Inspection Departments having jurisdiction may require ground- 
ing if they deem it necessary. 

Two-wire direct-current systems having no accessible neutral 
point are not to he, grounded. 
Alternating-Current Secondary Systems. 

b. Tarnsformer secondaries of distributing systems should 
preferably be grounded, and when grounded, the following 
rules must be complied with : — 

1. The grounding must be made at the neutral point 

or wire, whenever a neutral point or wire is ac- 
cessible. 

2. When no neutral point or wire is accessible, one side 

of the secondary circuit may be grounded, pro- 
vided the maximum difference of potential be- 



OUTSIDE WORK. 119 

tween the grounded point and any other point in 
the circuit does not exceed 250 volts. 
3. The ground connection must be at the transformers 
or on the individual service as provided in sec- 
tions c to g, and when transformers feed systems 
with a neutral wire, the neutral wire must also be 
grounded at least every 500 feet. 

Inspection Departments having jurisdiction may require ground- 
ing if they deem it necessary. 

Ground Connections. 

c. When the ground connection is inside of any building, 
or the ground wire is inside of, or attached to any building 
(except Central or Sub-stations), the ground wire must be 
of copper and have an approved rubber insulating covering 
National Electrical Code Standard, for from o to 600 volts. 

d. The ground wire in direct-current 3-wire systems must 
not at Central Stations be smaller than the neutral wire and 
not smaller than No. 6 B. & S. gage elsewhere. The ground 
wire in alternating-current systems must never be less than 
No. 6 B. and S. gage. 

On three-phase system, the ground wire must have a carry- 
ing capacity equal to that of any one of the three mains. 

e. The ground wire should, except for Central Stations 
and transformer sub-stations, be kept outside of buildings as 
far as practicable, but may be directly attached to the build- 
ing or pole by cleats or straps or on porcelain knobs. Staples 
must never be used. The wire must be carried in as nearly 
a straight line as practicable, avoiding kinks, coils and sharp 
bends, and must be protected when exposed to mechanical 
injury. 

This protection can be secured by use of approved conduit or 
moulding, and as a rule the ground wire on the outside of a build- 
ing should be in conduit or moulding at all places where it is within 
seven feet from the ground. 

f. The ground connection for Central Stations, trans- 
former sub-stations, and banks of transformers must be per- 
manent and effective and must include all available under- 
ground piping systems including the lead sheath of under- 
ground cables. 

g. For individual transformers and building services, the 
ground connection may be made as in Section f, or mav be 
made to water piping systems running into buildings. This 



120 MODERN ELECTRICAL CONSTRUCTION. 

connection may be made by carrying the ground wire into the 
cellar and connecting on the street side of meters, main cocks, 
etc. 

Where it is necessary to run the ground wire through any 
part of a building, unless run in approved conduit, it shall be 
protected by porcelain bushings through walls or partitions 
and shall be run in approved moulding, except that in base- 
ments it may be supported on porcelain. 

In connecting a ground wire to a piping system, the wire should 
be sweated into a lug attached to an approved clamp, and the clamp 
firmly bolted to the water pipe alter all rust and scale have been 
removed ; or be soldered into a brass plug and the plug forcibly 
screwed into a pipe fitting, or where the pipes are cast iron, into 
a hole tapped into the pipe itself. For large stations, where con- 
necting to underground pipes with bell and spigot joints, it is well 
to connect to several lengths, as the pipe joints may be of rather 
high resistance. 

Where ground plates are used ; a No. 16 Stubbs' gage copper 
plate, about three by six feet in size, with about two feet of 
crushed coke or charcoal, about pea size, both under and over it, 
would make a ground of sufficient capacity for a moderate-sized 
station, and would probably answer for the ordinary sub-station or 
bank of transformers. For a large central station, a plate with 
considerably more area might be necessary, depending upon the other 
underground connection available. The ground wire should be riv- 
eted to the plate in a number of places, and soldered for its whole 
length. Perhaps even better than a copper plate is a cast-iron plate 
with projecting forks, the idea of the fork being to distribute the 
connection to the ground over a fairly broad area, and to give a 
large surface contact. The ground wire can probably best be con- 
nected to such a cast-iron plate by soldering it into brass plugs 
screwed into holes tapped in the plate. In all cases, the joint be- 
tween the plate and the ground wire should be thoroughly protected 
against corrosion by painting it with waterproof paint or some 
equivalent. 



NOTE.— DO NOT FAIL TO SEE WHETHER ANY 
RULE OR ORDINANCE OF YOUR CITY CONFLICTS 
WITH THESE RULES. 

Class C. 
INSIDE WORK. 

(Light, Power and Heat. For signaling systems, see Class E.) 
ALL SYSTEMS AND VOLTAGES. 

General Rules. 

16. Wires. 

(See also Nos. 17, 18, 20, 26, 27, 44, 47 and 48. 
For construction rules, see Nos. 49 to 57.) 

a. Must not be of smaller size than No. 14 B. & S. gage, 
except as allowed for fixture work and pendant cord. 

For general purposes a wire smaller than No. 14 is too 
easily broken, either through a sharp kink or by drawing too 
tight with tie wires. To avoid trouble from kinks or sharp 
bends, wires smaller than 14 should preferably be stranded. 

b. Tie wires must have an insulation equal to that of the 
conductors they confine, and may be used in connection with 
solid knobs for the support of wires of size No. 8 B. & S. 
gage or over. Solid knobs or strain insulators must be used 
for all wires at the end of runs where conductors are ter- 
minated. Split knobs or cleats must be used for the support 
of conductors smaller than No. 8 B. & S. gage, except at the 
end of runs. 

Knobs or cleats which are arranged to grip the wire, must 



122 



MODERN ELECTRICAL CONSTRUCTION. 



be fastened by either screws or nails. If nails are used, they 
must be long enough to penetrate the woodwork not less than 




use screws for split knohs 



and cleats. 





Figure 62. 



one-half the length of the knob and fully the thickness of the 
cleat, and must be provided with washers which will prevent 
under reasonable usage, injury to the knobs or cleats. 



INSIDE WORK. 



123 



It is necessary where tie wires are used that they have an 
insulation the same as that of the conductor they confine. The 
tie wire often cuts into the insulation of the line wire and if 
it was not insulated it would become alive. The larger bear- 
ing surface given by the insulated wire will also reduce the 
liability of the tie wire cutting in. 

Formerly it was customary to use a solid knob and tie 
wire on all sizes of wire, but the present rule limits this type 
of knob to wires of No. 8 and larger. The main objection 
to the tie wire, especially with wires of small size, was the 



r — — 



- 




Figure 63. 



liability of the tie wire becoming loose and letting the line 
wire fall from the knob. This objection is overcome in the 
split knob where the wire is gripped directly by the porcelain 
knob itself. At the ends of runs the split knob must not be 
used but a solid knob as shown at (2), Figure 62, or a strain 
insulator as shown in Figure 63, may be used. Figure 62 
also shows other methods of supporting wires. At (4) is 
shown the manner of tying large wires of No. 8 B. & S. gage 
and larger; (6), shows a knot tied into the wire as is usual 
where the end of the wire connects into cut-outs or switches. 
At (5) insulators are arranged to hold large wires. It is not 
advisable to tie large wires to insulators as the weight of the 
wire will soon cause it to cut through the insulation. Cleats 
such as are shown at (8) and (9) are preferable. 



124 MODERN ELECTRICAL CONSTRUCTION. 

c. Must be so spliced or joined as to be both mechanically 
and electrically secure without solder. The joints must then 
be soldered unless made with some form of approved splic- 
ing device, and covered with an insulation equal to that on 
the conductors. 

Stranded wires (except in flexible cords) must be soldered 
before being fastened under clamps or binding screws, and 
whether stranded or solid, when they have a conductivity 
greater than that of No. 8 B. & S. gage they must be soldered 
into lugs for all terminal conections, except where an ap- 
proved solderless terminal connector is used. See Figure 54. 

On the left at the upper part of Figure 64 is shown the well- 
known Western Union joint. Before joining wires they should 
be thoroughly cleaned by scraping with the back of a knife or 
sand or emery paper. The insulation should be removed, as 
indicated at b; if it is cut into as at a, it is very likely that 
the wire will be "nicked" and will be likely to break at that 
point. It is also more difficult to tape a joint properly if the 
rubber has been cut in this way than it is with the rubber cut 
as at b. After the joint has been made it is covered with 
soldering fluid, a formula for which is given below. In lieu 
of this there are soldering sticks and salts, already prepared, 
on the market. 

The following formula for soldering fluid is suggested : — 

Saturated solution of zinc chloride 5 parts 

Alcohol 4 parts 

Glycerine 1 part 

The joint having been thoroughly covered with one of 
these preparations is next heated with a gasoline or alcohol 
torch and a small piece of solder allowed to melt on it near 
the center. It is well to avoid heating too much at the ends 
of the joint, as it weakens the wire. After the joint is partly 
cooled wipe off all moisture and cover with layers of rubber 
tape, enough, at least, so that it is equal in thickness to the 
rubber insulation on the wire used, as shown at a and b. If 



INSIDE WORK. 



125 



H\\\VP^\\\W-«*J| 




126 MODERN ELECTRICAL CONSTRUCTION. 

the rubber tape is put on before the wire has entirely cooled 
the remaining heat will assist in vulcanizing the rubber. This 
rubber tape is then covered with friction tape to keep it in 
place. Before taping joints the outer braid of the wire should 
be carefully skinned back. If any of the cotton threads of 
which it consists were to be left in contact with the bare wire, 
they would, when moist, form a leak, which might prove 
troublesome. If joints are exposed to the weather it will be 
well to paint them over with some insulating paint to keep 
the friction tape in place, as it will otherwise soon work loose 
when it becomes dry. 

At c and d "tap" joints are shown. The method shown 
at d is preferable, because the wire cannot easily work loose. 
The method of joining shown at e is useful when, for in- 
stance, two wires, each of which is fastened to an insulator, 
are to be joined. The wires can be drawn very tight in this 
way. This sort of joint is very common in fixture work, and 
should be finished off as at f. 

Twin wires other than flexible cord are allowed only in 
metal conduits, and joints in them should be made only 
within the junction boxes. When joints in a twin wire are 
unavoidable, the wires should be joined as at g, so that the 
joints are not opposite each other. Joints in flexible cord 
should be avoided. 

In splicing stranded wires it is customary to remove some 
of the center strands to avoid making a very bulky splice. All 
stranded wires must be soldered where fastened under bind- 
ing screws. The rule does not require the soldering of flex- 
ible cords. Formerly this was required by the rules but it 
has been found that more harm than good is done for if the 
soldering was not done very carefully the fine wire strands 
were made brittle and would break off. It was also found 
that the insulation was destroyed for some distance from the 
point of soldering. The lining of a socket should be so de- 



INSIDE WORK. 



127 



signed as to thoroughly protect any stray strands which may 
protrude from the wire under the binding post from coming 
in contact with the metal of the socket. If it is desired to 
solder the ends of the cord before fastening under binding 
posts this is best done by dipping the ends into molten solder 
taking care that the copper is cooled before it has had time 
to heat the rubber insulation. 

Figure 65 shows lead covered wire spliced and taped, In 
handling lead covered wire great care must be exercised (es- 
pecially with paper insulated) that it be not bruised and the 
lead not punctured. The lead covering is of use only as a 
protection against water; if it admits the least bit of mois- 
ture it is worse than useless. In cutting the lead off from the 
end of the cable great care should be taken that the insula- 
tion is not injured. The best practice is to cut the lead only 
partly through then, by slightly bending the cable, break the 
lead and pull it off. 

The ends of lead covered wires should always be kept 
sealed until ready for use ; in damp places the paper insula- 
tion may absorb moisture, which will ground the wire on the 
lead. When installed the ends should always be sealed against 



^-M^w^^m^m 



Figure 65. 



moisture. Lead covered wires should never be used where 
there is a liability of rails being driven into them. 

Joints in lead covered wires are made just as in ordinary 
wires. Extreme care is necessary that no moisture be left on 
the wire when it is taped or covered up. Before the wire is 
joined a sleeve (Figure 65) is slipped over one of the wires. 



128 MODERN ELECTRICAL CONSTRUCTION. 

After the joint has been made and taped, this sleeve is placed 
so as to cover it, and the ends hammered down to fit close 
against the lead on the wires. That part of the lead which 
must be soldered to make the joint watertight is scraped until 
it is perfectly bright and then coated with tallow candle 
grease. It can then be soldered with an iron, or melted solder 
can be poured on it and wiped around it, as plumbers do. If 
a soldering iron is used it must not be too hot and not allowed 
to remain in one place too long, as the lead itself melts at 
nearly the same temperature as the solder. An inexperienced 
workman may burn more holes into the lead than he closes. 
If a neat job is desired, that part of the lead which is to be 
kept free of solder is covered with lampblack and glue, or 
ordinary paper hanger's paste, or a mixture of flour and water 
boiled, so as to prevent the solder from taking on it. 

A Western Union joint, as shown in Figure 65, is some- 
what objectionable in lead covered wires on account of the 
amount of space required by the joint itself. If this form of 
connection is used it is generally necessary to provide a lead 
sleeve somewhat larger than the outside diameter of the lead 
covering of the wire and the end of this sleeve must then be 
tapered down to conform to the lead covering. To overcome 
this objectionable feature joints are made as shown in Fig- 
ure 66, where (a) shows a copper sleeve slipped over the ends 




Figure 66. 

of the wire, the whole being thoroughly soldered. The wires 
may be either butted together or lapped as shown by the dot- 
ted lines. In place of the metal sleeve the ends of the wires 
may be lapped and bound together by a small copper wire 



INSIDE WORK. 129 

as shown at (b), the whole being soldered; this, however, is 
not as strong a joint as that made with a sleeve. Large 
stranded cables are joined as shown at a, Figure 66 or they 
may be joined as shown at the lower part of Figure 64. 

d. Must be separated from contact with walls, floors, tim- 
bers or partitions through which they may pass by non-com- 
bustible, non-absorptive, insulating tubes, such as glass or 
porcelain, except at outlets where approved flexible tubing is 
required. 

Bushings must be long enough to bush the entire length 
of the hole in one continuous piece, or else the hole must first 
be bushed by a continuous waterproof tube. This tube may 
be a conductor, such as iron pipe, but in that case an insulat- 
ing bushing must be pushed into each end of it, extending 
far enough to keep the wire absolutely out of contact with the 
pipe. 

e. Where not enclosed in approved conduit, moulding or 
armored cable and where liable to come in contact with gas, 
water, or other metallic piping or other conducting material, 
must be separated therefrom by some continuous and firmly 
fixed non-conductor creating a permanent separation. Must 
not come nearer than 2 (two) inches to any other electric 
lighting, power or signaling wire, not enclosed as above, with- 
out being permanently separated therefrom by some contin- 
uous and firmly-fixed non-conductor. The non-conductor 
used as a separator must be in addition to the regular insula- 
tion on the wires. Where tubes are used, they must be se- 
curely fastened at the ends to prevent them from moving 
along the wire. 

Deviations from this rule may, when necessary, be allowed 
by special permission. 

The reasons for the separation of wires from everything 
but their insulating supports are many. Should a bare live 
wire come in contact with damp woodwork or masonry, there 
would very likely be some flow of current to ground and 
through the ground to the other pole of the dynamo or other 
wire. This flow of current may gradually char the wood- 
work, and in time start a fire; or it may gradually eat away 



130 



MODERN ELECTRICAL CONSTRUCTION. 



the wire, finally causing it to break. When a wire is eaten 
away, as shown at c and e, Figure 67, if it is carrying much 
current, the thin part will become very hot and will set fire to 
whatever inflammable material may be near it. If the current 
flow to the ground continues, the positive wire will finally be 
entirely severed, and an arc, similar to" that noticed in an 
ordinary arc lamp, will be established, and will continue until 
the wire has been burned away and the space between the two 




Figure 67. 



ends becomes too great for the arc to maintain itself. The 
negative wire, to which the current flows, is not eaten away 
in this manner, and such current flow is only possible when 
two wires of a system are in electrical connection with the 
ground. This action may, however, occur, even if the two 
grounded wires are miles apart. Wires and gas pipes are 
often destroyed through intermittent contact ; for instance, if 
a wire makes a good contact to a gas pipe and there is a small 
leak to the pipe no particular harm will be done as long as 
the contact remains good. Should, however, the contact be 



INSIDE WORK. 131 

intermittent, there will be a small arc at each break, and this 
will, little by little, burn holes into the gas pipe and into the 
wire. This action will take place on either a positive or 
negative wire. Non-combustible supports for wires are fur- 
ther useful in that they tend to prevent flames from the rub- 
ber insulation (which is very easily ignited from any of the 
above causes, from spreading to surrounding material. 

Figure 67 consists of copies of specimens showing effects 
of electrolysis, short circuits, and heating of lamp. These il- 
lustrations are copied from fire reports of the National Board 
of Underwriters. 

At a is shown a piece of gas pipe, which had been sub- 
ject to electrolytic action until finally a hole had been eaten 
through the metal ; b is a socket which had been short cir- 
cuited, and the excessive damage was due to overfusing of 
circuit. 

At c and e, the effects of electrolysis on wire are shown ; 
c is a piece of underwriter's wire (not approved in moulding), 
which had been used in damp moulding, the leak to ground 
through the dampness causing the gradual eating away of the 
wire; c shows a breakdown in the insulation and subsequent 
electrolytic action on the wire causing it finally to break. 
This wire had been used in a roundhouse, where the sulphur 
fumes and the condensation of escaping steam on insulators 
had formed a path to ground. At d is an incandescent lamp 
which had been covered with a towel, the confined heat soft- 
ening the glass and setting fire to the towel. The danger of 
fire from overheated lamps is much greater than is generally 
supposed. Small lamps and lamps subject to a little excess 
of voltage are especially dangerous, and many instances are 
on record where they*have charred woodwork and set fire to 
cloth or paper shades. 

It may in many cases seem unnecessary to have bushings 
in one piece long enough to pass through a floor, or wide 



132 



MODERN ELECTRICAL CONSTRUCTION. 



wall; but especially in passing through floors, it is easily pos- 
sible for wires to become crossed between the joists; that 
is, the wire entering at the right above the floor may be 
brought out at the left below the floor and the other wire 
through the opposite holes. In such a case the two wires of 
opposite polarity will be in contact, and should the insulation 
give out from any cause whatever, such as abrasion, or the 




Figure 68. 



Figure 69. 



Figure 70. 



gnawing of rats and mice, there would be nothing to prevent 
a short circuit and consequent fire. In passing through floors 
or walls the wires often come in contact with concealed pipes 
or other grounded material, so that only by making the bush- 
ings continuous as shown in Figure 68 can the wires be prop- 
erly protected. 

Figure 69 shows short bushings arranged in iron pipe. 
Figure 70 shows a case where there is an offset in the wall. 
Cases of this kind very often occur. Sometimes the floor can 
be taken up and an iron conduit, propejly bent, put in place ; 
the wires being reinforced with flexible tubing; or the wires 
placed on insulators. In this latter case the floor must not be 
put down until the inspector has examined the wires. The 



INSIDE WORK. 



133 



wires may be run on top of the floor to such a place where 
a continuous bushing may be dropped through the floor. The 
wires on top of the floor must be then protected by a suitable 
boxing of at least the same dimensions as given for boxing 
on side walls. 

Caution must be observed in placing wires carrying alter- 
nating currents in single conduits or pipes. If the wires 
carry only a small amount of current no serious effects will 
result but if considerable current is flowing over the wires 
the pipes may become very hot. Where it is necessary to use 
pipe or conduit for bushings in such cases both wires should 
be placed in the same pipe. 

Figure 71 is a sectional view of the manner in which wires 
are usually run through joists in bushings. For small wires 




Figure 71. 



bushings should preferably be installed as shown at top ; never 
as shown in the middle row. For larger wires the holes 
must be bored as straight as possible ; otherwise it will be 
difficult to pull wires through. The quantity of wire needed 
is also somewhat increased by slanting the holes. In open 
places wires are generally installed on insulators as shown- in 
Figure 72. 

Figure 72 shows different methods employed where one 
wire crosses another. The method at the left, which is more 
suited to large stiff wires, does not quite comply with the 
rule, but is very often used. The other two methods are 



134 



MODERN ELECTRICAL CONSTRUCTION. 



preferable. Insulating supports should always be provided at 
the place of crossing to prevent the upper wires from sag- 
ging and resting on the lower ; also to prevent any strain from 
coming on tap joints. Approved flexible tubing such as cir- 
cular loom is also often used in crossing wires and pipes. In 




Figure 72. 



dry locations it is quite safe and does not break as easily as 
tubes, but should never be used where there is any likelihood 
of dampness. 

/. Must be so placed in wet places that an air space will 
be left between conductors and pipes in crossing, and the for- 
mer must be run in such a way that they cannot come in con- 
tact with the pipe accidentally. Wires should be run over 
rather than under pipes upon which moisture is likely to gather 
or which, by leaking, might cause trouble on a circuit. 

This is a rule that is very often violated, as much work is 
done using loom, as shown at the left of Figure 73, and is 
quite safe with gas pipes. With cold water pipes, which are 
likely to sweat, or with steam pipes, it is very bad practice. 
Where pipes are close against a ceiling it is better either to 
fish over them or drop wires some distance below them as 
illustrated at the right of the figure. No part of the wiring 



INSIDE WORK. 135 

should be in contact with pipes. On side walls where vertical 
wires run across horizontal pipes the only safeguard would 
be to box the pipes and run the moisture to one side. The 
most harm is done by water on the insulators. If these can 
be kept dry it does not matter much about wires which hang 
free in the air. Whatever form of insulation is used in cross- 
ing pipes, it must be continuous. Short bushings strung on 
the wire, where a large pipe or number of pipes are being 
crossed, is not satisfactory, as the bushings are apt to separate 



7^^^^^^^^!^^^^ T% 





Figure 73. 

or moisture gather in the space between them. The insula- 
tion must also be firmly attached to the wires. If knobs are 
not used as shown in Figure 72 to keep the bushings in place, 
they must be taped to the wire. 

g. The installation of electrical conductors in wooden 
moulding, or on insulators, in elevator shafts will not be ap- 
proved, but conductors may be installed in such shafts if en- 
cased in approved metal conduits, or armored cable. 

Wires supported on insulators in such places are very likely 
to be disturbed, especially in freight elevators. Moulding is 
often so impregnated with oil and the draft in an elevator 
shaft is usually so strong that a blaze once started would 
quickly run to the top. 

17. Underground Conductors. 

a. Must be protected against moisture and mechanical in- 
jury where brought into a building, and all combustible ma- 
terial must be kept from the immediate vicinity. 

b. Must not be so arranged as to shunt the current 
through a building around any catch-box. 



136 



MODERN ELECTRICAL CONSTRUCTION. 



By reference to Figure 74 the meaning of this rule will 
be made clear. With wire run as shown it would be easy for 
any one having disconnected one service switch to believe all 
wires in the building dead, while they were in reality still 
being kept alive by the other switch. This connection would 
allow current to pass from one street main to another with- 
out going through the fuses in the street catch-box. 



AllStrectM^ins 
/Fused Here 




1 



pmm%wpvwm^ 



Figure 74. 



c. Where underground service enters building through 
tubes, the tubes shall be tightly closed at outlets with asphalt- 
um or other non-conductor, to prevent gases from entering 
the building through such channels. 

d. No underground service from a subway to a building 
shall supply more than one building except by written permis- 
sion from the Inspection Department having jurisdiction. 

18. Table of Carrying Capacity of Wires. 

(See tables in back of book.) 

19. Switches, Cut-outs, Circuit-Breakers, Etc. 

a. On constant potential circuits, all service switches and 
all switches controlling circuits supplying current to motors 



INSIDE WORK. 137 

or heating devices, and all fuses, unless otherwise provided 
(for exceptions as to switches see Nos. 8 c, 25 a and 43 c; 
for exceptions as to cut-outs see No. 23 a and b, must be 
so arranged that the fuses will protect and the opening of the 
switch will disconnect all of the wires ; that is, in the two- 
wire system the two wires, and the three-wire system the 
three wires, must be protected by the fuses and disconnected 
by the operation of the switch. 

When installed without other automatic overload pro- 
tective devices automatic overload circuit breakers must have 
the poles and trip coils so arranged as to afford complete pro- 
tection against overloads and short circuits, and if also used 
in place of the switch must be so arranged that no one pole 
can be opened manually without disconnecting all the wires. 

This, of course, does not apply to the grounded circuit of 
street railway systems. 

The exceptions for switches are for motors of Y\ H. P. 
or less on circuits where the voltage does not exceed 300, elec- 
tric heaters requiring not more than 660 watts and electric 
cranes. In the first two cases single pole switches may be 
used and in the case of cranes switches need not be provided 
for each individual motor. The exception for cut-outs is 
for mains where the fuse is omitted in the neutral wire. 

In connecting double pole snap switches the wireman 
should be very careful. Most of these switches cross polarities 
as shown in Figure 75, and if connected wrong will form short 
circuits. Many of them have been connected this way even 
by wiremen of some experience. 

b. Must not be placed where exposed to mechanical injury 
nor in the immediate vicinity of easily ignitible stuff or where 
exposed to inflammable gases or dust or to flyings of com- 
bustible material. 

Where the occupancy of a building is such that switches, 
cut-outs, etc., cannot be located so as not to be exposed as 
above, they must be enclosed in approved dust-proof cabinets 
with self-closing doors, except oil switches and circuit breakers 
which have dust-tight casings. 



138 



MODERN ELECTRICAL CONSTRUCTION. 



Whenever an electric current is broken, whether by fuse 
or switch, an arc varying with the current strength is formed. 
Should a switch be only partly opened, this arc will continue 
and consume the metal of the switch until the gap in which 
it burns becomes too long, when the current will be broken. 





Figure 75. 



Figure 76. 



Meanwhile there is much heat generated which may readily 
communicate to inflammable material near by. 

There seems to be no reason except economy of wire why 
cut-outs should ever be placed inside of dust rooms. Switches 
of course must often be placed in such rooms, as in many 
cases the entire building outside of the engine room is dusty. 
In such cases the switches as well as the cut-outs may, how- 
ever, be often placed on the outside walls convenient to some 
window. 

An approved cabinet is shown in Figure 76. If used in 
connection with knife switches it should be large enough to 
admit being closed when the switch is open. In cases where 
cut-outs and switches must be located in dusty rooms, it 
would be well to construct double cabinets, one part for the 
cut-outs and another for the switches. The fuses, which are 



INSIDE WORK. 



139 



the most dangerous, can then be tightly enclosed, as it .will 
seldom be necessary to get at them. In practice it has been 
found almost impossible to keep the doors of cabinets which 
are much used closed. It seems next to impossible to con- 
struct a cabinet which is dustproof, with a door that can be 
readily opened, and a self-closing door can hardly be made to 
remain dustproof. Doors are made self-closing either through 
gravity or by suitable springs. 

As switch and cut-out boxes are very likely to be used for 
the storage of cotton waste, paper, etc., which would readily 




Figure 77. 



ignite from a melted fuse, it would be well to construct them 
with a slanting bottom as indicated in Figure 77, so that noth- 
ing will lie in them. 

A cut-out box of very good design is shown in Figure 77. 
The door closes by gravity and the manner in which it lies 
against the cabinet causes it to close more securely than it 
would if hung perpendicularly. 

c. Must, when exposed to dampness, either be enclosed 
in a moisture-proof box or mounted on porcelain knobs. The 



140 MODERN ELECTRICAL CONSTRUCTION. 

cover of the box must be so made that no moisture which 
may collect on the top or sides of the box can enter it. 

Figure 77 is a sectional side view of a cut-out box for use 
out of doors. It is mounted on porcelain knobs. In all damp 
places much trouble is experienced from leakage through the 
moisture on the surface of the slate or marble and through 
the wax used to cover the bare parts on back of switch. 

In locations where moisture is always present an in- 
candescent lamp burned in the cut-out box will tend to keep 
it dry. This system has been used in packing houses and has 
proven very satisfactory. 

d. Time switches, sign flashers and similar appliances 
must be of approved design and enclosed in an approved 
cabinet. 

Special attention should also be given to the location of 
such switches and flashers. They are often left without care, 
the blades, wear down and the arcing continues through bad 
contacts. Often springs become weak and no longer break 
the circuit properly. 

Time switches are usually operated by clockwork, the 
clock releasing a spring which throws the switch on or off as 
may be required and pre-determined. Complete diagrams of 
sign flashers are given in "Modern Wiring Diagrams and De- 
scriptions" and will not be repeated here. 



CONSTANT-CURRENT SYSTEMS. 

/rincipally Series Arc Lighting. 

(See also Nos. 16, 17, 18 and 44. For construction rules, see 

Nos. 49 and 50.) 

20. Wires. 

a. Must have an approved rubber insulating covering. 

b. Must be arranged to enter and leave the building 
through an approved double-contact service switch mounted 
in a non-combustible case, kept free from moisture, and easy 
of access to police or firemen. 

In order that all of the wiring in the building may be en- 
tirely disconnected a switch, the principle of which is illus- 




Figure 78. 



trated at d, Figure 78, is provided where w r ires enter and 
leave the building. A modern commercial form of this switch 
is shown in Figure 79. This switch never breaks the circuit. 
As shown in Figure 78, the current passes from the positive 
poles, through the upper blade of the switch to b and thence 
through the arc lamps back to c and to the negative pole. 
When it is desired to extinguish the lamps the two blades of 



142 



MODERN ELECTRICAL CONSTRUCTION. 



the switch are moved downward, as indicated by the dotted 
lines. The contacts d are arranged so that both switch blades 
connect with them before disconnecting entirely from the 
points b and c. As soon as both blades are in contact with d 
all current flows through it because the resistance of it is 
so very much less than that of the lamps. With the switch 
in the position indicated by dotted lines, the current still flows 
in the outside wires, but all wires within the building are 
"dead." At e, Figure 78, is shown a single-pole switch which 
operates on the same principles as the other. If this switch is 
closed all current will pass through it; if open the current will 

pass through the last 
lamp. A switch of this 
kind is always arranged 
within the lamp itself. 
This latter way of 
switching lamps should 
never be used, as a lamp 
switched in this way is 
never safe to handle. 
There is just as much 
danger from shocks 
when the 1 a m p is 
switched off as when on. 
With switches as de- 
scribed above there is no 
spark whatever whan lamps are switched off, but there is usu- 
ally quite an arc when the lamps are switched in. Should 
there be a broken wire or a lamp out 'of order in the circuit 
to be switched in, there will be quite an arc maintained for 
some time. In such a case the switch should be quickly closed 
and the trouble located. 

In handling live wires of this system great care is neces- 
sary. The wireman should insulate himself from the ground 



mwm 





Figure 79. 



CONSTANT CURRENT SYSTEMS. 143 

by a dry board, or, if all about him is damp, by a board rest- 
ing on insulators. Rubber gloves and rubber boots, if kept 
dry, are useful. 

Death or bad burns may result if the wireman, standing 
on wet ground or any conductor in connection with it, touches 
part of a circuit which is also partly in connection with the 
ground. If, in Figure 78, the wire at f is grounded, a man in 
connection with the ground and touching a bare wire at h will 
receive a shock due to about 50 volts, but if he touches the 
wire at g he will receive a shock of about 150 volts. The 
shock received from a line containing 100 lamps may be any- 
thing from 50 to 5,000 volts, and may result in only a slight 
burn or in instant death. 

Another danger in connection with live circuits is the 
liability of cutting oneself into circuit. If one is perfectly 
insulated from the ground there is no harm whatever in touch- 
ing one live wire ( with very high voltages such insulation is, 
however, hard to obtain) with either one or both hands while 
the wires are in order. Should, however, the wire between 
the two hands break, the current would immediately pass 
through the body, very likely causing instant death. Even if 
the circuit is not entirely broken, if only a resistance is cut 
in, the shock will be very severe. As, for instance, if one 
should touch the terminal of an arc lamp, not burning, with 
each hand nothing whatever would be felt, but, if the lamp 
were now suddenly switched on, there would be a very severe 
shock at first, which would become less so when the lamps 
were fairly started. To avoid the possibility of such occur- 
rences when wofking on live lamps or circuits a short wire 
known as a "jumper" is often connected, as at k, Figure 78. 
This will carry all current, and there is now no danger except 
from a connection to ground. 

c. Must always be in plain sight, and never encased, ex- 
cept when required by the Inspection Department having 
jurisdiction. 



144 MODERN ELECTRICAL CONSTRUCTION. 

What is known as concealed knob and tube work is not al- 
lowed in wiring for high tension arcs; neither can the wires 
be run in moulding or conduit. 

It has been customary to use no smaller than No. 6 wire 
for these high tension series circuits. The current required 
is seldom more than 10 amperes, and No. 14 wire has suffi- 
cient carrying capacity, but its mechanical strength is not very 
great. The danger from a broken wire in high tension sys- 
tems is much greater than in low tension systems, because of 
the long arc which occur at the break. The loss in volts per 
100 feet with No. 6 will be about .4, while with No. 14 it will 
be 2.6. While this will not affect the lights, the pressure at 
the generator being correspondingly increased, the question 
of drop is of importance. On a circuit 10 miles long a No. 
14 wire would have a drop of 1372 volts and a No. 6 wire 
a drop cf 211 volts. 

d. Must be supported on glass or porcelain insulators, 
which separate the wire at least one inch from the surface 
wired over, and must be kept rigidly at least eight inches from 
each other, except within the structure of lamps, on hanger- 
boards or in cut-out boxes, or like places, where a less distance 
is necessary. 

An extra precaution often taken in this kind of work on 
plastered walls is to place a wooden block or rosette about 
three inches in diameter and one-half inch thick under each 
insulator; this secures greater separation from ceilings and 
side walls and adds greatly to the stability of the insulators. 
On plastered walls a small insulator, if subjected to side 
strain, will cut into the plaster on one side and allow the 
wires to sag; the wooden block will prevent this. 

e. Must, on side wall, be protected from mechanical in- 
jury by a substantial boxing, retaining an air space of one inch 
around the conductors, closed at the top (the wires passing 
through bushed holes), and extending not less than seven 
feet from the floor. When crossing floor timbers in cellars, 



CONSTANT CURRENT SYSTEMS. 



145 



or in rooms where they might be exposed to injury, wires 
must be attached by their insulating supports to the under 
side of a wooden strip not less than one-half an inch in thick- 
ness. Instead of the running-boards, guard strips on each 
side of and close to the wires will be accepted. These strips 




Figure 80. 



to be not less than seven-eighths of an inch in thickness and 
at least as high as the insulators. 

Figure 80 is an illustration of protection on side walls, 
giving the dimensions required for high tension. The wooden 
block shown, which raises bushings above floor, is an extra 
protection to prevent water from running into them. 



I46 MODERN ELECTRICAL CONSTRUCTION. 

21. Series Arc Lamps. 

(For construction of Arc Lamps, see No. 74.) 

a. Must be carefully isolated from inflammable material. 

b. Must be provided at all times with a glass globe sur- 
rounding the arc, and securely fastened upon a closed base. 
Broken or cracked globes must not be used. 

c. Must be provided with a wire netting (having a mesh 
not exceeding one and one-fourth inches) around the globe, 
and an approved spark arrester (see No. 75), when readily 
inflammable material is in the vicinity of the lamps, to prevent 
escape of sparks of carbon or melted copper. 

Outside arc lamps must be suspended at least eight feet 




Figure 81. 

above sidewalks. Inside arc lamps must be placed out of 
reach or suitably protected. 

Arc lamps, when used in places where they are exposed 
to flyings of easily inflammable material, must have the car- 
bons enclosed completely in a tight globe in such manner as 
to avoid the necessity for spark arresters. 

"Enclosed arc" lamps, having tight inner globes, may be 
used, and the requirements of Sections b and c above would, 
of course, not apply to them. 

d. Where hanger-boards are not used, lamps must be hung 
from insulating supports other than their conductors. 

e. Lamps when arranged to be raised and lowered either 
for carboning or other purposes, shall be connected up with 
stranded conductors from the last point of support to the 
lamp, when such conductor is larger than No. 14 B. & S. gage. 



CONSTANT CURRENT SYSTEMS. 



147 



Figure 81 shows the usual method of suspending out- 
door arc lamps on buildings. The supporting wire 
may be fastened to brick or stone walls by drilling a hole 
about four inches deep and plugging this securely with wood, 
when an eye or lag bolt or large spike may be driven or 
screwed into it. Expansion bolts, of which there are many 
kinds to be had, may also be used and are preferable in most 
cases. It is best to arrange the supporting wires at quite a 
high angle, otherwise the direct outward pull may be too 
great. 

On very low ceilings, lamps are often arranged as shown 
at Figure 82, the plastering being cut away and lamp sus- 




Figure 82. 



pended from floor above joists. The space above plaster must 
be enclosed on all sides and all woodwork protected with as- 
bestos board at least one-eighth inch thick. 

If this method is used with constant potential arc lamps 
carrying resistance in the hood, it would be well to remove 
or short-circuit this resistance and locate another in a more 
suitable place. 

A stranded wire is required for lamps that are to be raised 
or lowered as the constant movement of the wires due either 
to the raising or lowering of the lamp for recarboning or the 
swinging of the wires by the wind is liable to cause them to 
break and form an arc inside the insulation. 



I48 MODERN ELECTRICAL CONSTRUCTION. 

22. Incandescent Lamps in Series Circuits. 

a. Must have the conductors installed as required in No. 
20, and each lamp must be provided with an automatic cut-out. 

b. Must have each lamp suspended from a hanger-board 
(see Nq. J2>) by means of rigid tube. 

c. No electro-magnetic device for switches and no mul- 
tiple-series or series-multiple system of lighting will be ap- 
proved. 

d. Must not under any circumstances be attached to gas 
fixtures. 

Some years ago carbon filament series incandescent lamps 
were frequently used for street lighting, especially in small 
towns and in the residence districts of cities. These lamps 
were operated in series direct from the primary circuits with 
either automatic cutouts at the lamps or an arrangement in 
the plant whereby additional lamps could be switched in on 
the circuit as lamps burned out on the line. They were also 
operated in connection with series arc lamps on the same cir- 
cuits. They were seldom used for inside lighting. None of 
these systems proved very satisfactory. 

With the advent of the tungsten lamp the use of series 
lighting has greatly increased for the purposes mentioned. 
These lamps may be obtained of various candle powers and 
are made with a very rugged filament. They are operated in 
series on alternating current circuits with current transformers 
or current regulators. 

Each lamp is inserted in a special socket such as is shown 
in Figure 83. The socket is constructed of porcelain so that it 
is perfectly weatherproof and is provided with a pair of metal 
prongs arranged to fit into the receptacle as shown. Inserted 
between the prongs is a thin film of shellac or mica. Cur- 
rent flows from the contacts on the receptacle through one of 
the prongs to the lamp and out through the other prong. If 
the lamp burns out an excessive voltage is impressed on the 
terminals and the insulating film is broken down the circuit 
being then completed directly through the metal prongs. 



CONSTANT CURRENT SYSTEMS. 



149 



The socket may be removed from the receptacle in which 
case the circuit closes automatically by the spring clips of the 
receptacle coming together. A new lamp may then be inserted 
and a new film placed between the prongs and the lamp then 
put in service. Removing the lamp from the socket allows the 
spring contact inside the socket to close the circuit so that the 




socket 



^k^Mi -^ W^l 



^^^^M 




Figure 83. 



lamps may be changed at will. The automatic film will break 
down at a potential of about 400 volts. 

The same precautions for handling these circuit must be 
observed as mentioned in the case of series arcs. 

Considerable discussion has arisen at times in regard to the 
rule restricting series-multiple or multiple-series systems of 
lighting. This rule has been applied to low potential systems 
circuits but it will be noted that it comes under the head of 
constant current systems (principally series arc lighting) and 
was not intended to refer to the ordinary low potential 
systems. 

The table given below gives data on the Mazda Street 
series lamps. 



150 



MODERN ELECTRICAL CONSTRUCTION. 
MAZDA STREET SERIES LAMPS. 



Ampere 
Range? 


Candle- 
power 


Average 
Total 
Watts 


Average 
Volts 


W P. c. 


% Spherical 
of Horizontal 
Candle-power 


Total 
Lumens 


Hours 
Life 


4.0 
(3.9 to 4.3) 


32 

60 
100 
200 
350 


37.8 

70.8 
118.0 
2360 
413.0 


9 5 
17.7 
29.5 
59. p 
103.3 


1.18 
1 18 
1.18 
1.18 
1.18 


78.3 


816 
690 
984 
1968 
S448 


1350 


5.5 

(5.1 to 6.9) 


32 
60 
1C0 
200 
350 


378 
70.8 
118.0 
236.0 
413.0 


6.9 
12.9 
21 4 
42.9 
75.1 


1.18 
1.18 
1.18 
1.18 
1.18 


78.3 


m 

690 

984 

1968 

3443 


1360 


••• 

(6.1 to 6.9) 


32 

60 

100 

200 

350 


37.8 
70.8 
118.0 
236.0 
413.0 


5 7 
10.7 
17.9 
35.8 

62.6 


1.18 
1.18 
1 18 
1.18 
1.18 


78.3 


315 
690 
984 
1968 
3443 


1350 



CONSTANT-POTENTIAL SYSTEMS. 
General Rules — All Voltages. 

23. Automatic Cut-Out (Fuses and Circuit-Breakers). 

(See also No. 19. For construction rules see Nos. 66 and 67.) 

The fuse is the principal protective device used in electric 
light and power work. In its simplest form it consists of a 
piece of wire made of a certain alloy designed to melt at 
a comparatively low temperature. It is so connected in the 
circuit that all the current must pass through it. We have 
already seen that currents of electricity generate heat in the 
conductors through which they pass, and that this heat is pro- 
portional to the square of the current flowing; that is, if we 
double the current we shall increase the production of heat 
fourfold. A dangerous rise in current strength may be due 
to a "short circuit" or to an overload, too many lamps or 
motors being connected to a circuit. To prevent damage to 
wires and other apparatus from excessive currents, fuses or 
cut-outs must be installed. When the current rises above its 
allowed strength the fuse melts and opens the circuit; that 
is, stops all current flow. The melting of the fuse is accom- 
panied by a flash of fire due to the arc which is set up across 
the break in the fuse wire. On an ordinary overload with the 
smaller size fuses this arc may not be very severe, but with 
the larger size fuses and on short circuits a very severe flash 
and explosion may result and molten metal may be thrown 
for some distance from the fuse. This explosion is caused by 
the outer layers of metal of the fuse remaining cool and in 
a solid state while the metal at the center of the fuse is first 
melted and then vaporized. 

Another device which is used for the same purpose as the 



152 MODERN ELECTRICAL CONSTRUCTION. 

fuse is known as the circuit-breaker. A circuit-breaker in 
its simplest form comprises a knife switch which when closed 
is forced in against a spring and held in place by means of 
a small catch. A solenoid, inside of which is placed a move- 
able iron core, is connected in series with one side of the 
switch. When the current passing through this solenoid ex- 
ceeds a certain amount, the iron core is drawn up into it, and, 
striking against the catch, releases the switch which will then 
fly open, thus cutting off the current. The core of this sole- 
noid is so designed that when it starts to move its speed is 
greatly accelerated so that it strikes the catch a sharp blow. 
By means of a small adjusting screw the circuit-breaker can 
be set to operate at various current strengths within its limits. 
For this reason and for the further reason that it is so eas- 
ily made inoperative by tying or blocking its solenoid it is not 
approved for general use unless fuses are also installed. It 
may be used under the care of a competent electrician who 
understands the dangers of its abuse. 

Under these conditions its use is to be strongly recom- 
mended. Where not so used fuses must also be provided in 
the same circuit with the circuit breaker. For further infor- 
mation in reference to the use of circuit breakers see section 
on Generators, Page 58. 

a. Must be placed on all service wires, either overhead or 
underground, in the nearest accessible place to the point 
where they enter the building and inside the walls, and ar- 
ranged to cut off the entire current from the building. 

» Where the switch required by No. 24 a is inside the build- 
ing, the cut-out required by this section must be placed so as 
to protect it. 

For three-wire (not three-phase) systems the fuse in the 
neutral wire may be omitted, provided the neutral wire is of 
equal carrying capacity to the larger of the outside wires, 
and is grounded as provided for in No. 15. 

In risks having private plants, the yard wires running from 
building to building are not considered as service wires, so 



CONSTANT-POTENTIAL SYSTEMS. 



153 




that cut-outs would not be required where the wires enter 
buildings, provided that the next fuse back is small enough to 
properly protect the wires inside the building in question. 

The fuse block here required serves a double purpose ; it 
affords protection to the whole installation while in use, and 
is an effective means of disconnecting a building when cur- 
rent is no longer used. This can also be accomplished by 
means of the service switch, but a switch 
is so easily closed by any one that it must 
never be relied upon entirely for this 
purpose. 

Figure 84 shows arrangement of fuses 
and switch as commonly installed where 
wires enter buildings. The wires enter at 
the top, connect to the fuse terminals, cur- 
rent passing through the fuses to the 
switch. 

Figure 84. This rule allows the neutral fuse to be 

omitted on three-wire systems where the neutral is grounded 
and where the neutral wire is of as great carrying capacity 
as the larger of the outside wires. On three-wire systems 
where the neutral wire is not grounded, as in the case of some 
isolated plants, fuses must be placed in all three wires, includ- 
ing the neutral wire. The reason for this is obvious. A 
ground coming on any part of the neutral wire of a three- 
wire grounded system cannot cause a short circuit. Referring 
to Figure 85, G shows the permanent ground and b a ground 
on any other point on the neutral wire. It is plain that the 
ground b cannot cause a short circuit, and the fuse in this 
wire may, therefore, be omitted. A ground coming on 
either of the outside wires, at a for instance, would be cleared 
by the fuse protecting that wire. In a system with an un- 
grounded neutral a single ground coming on one of the out- 
side wires,, as at g' for instance, would not cause a short cir- 



/54 



MODERN ELECTRICAL CONSTRUCTION. 



cuit, but if the outside wire was grounded at g' and a ground 
should come on the neutral wire, at b for instance, a short 
circuit would immediately result and the neutral wire would 
probably be destroyed owing to the fact that there is no fuse 
to protect it. 

If the fuse is omitted in the neutral wire and a fuse on 
one of the outside mains should blow, the neutral wire would 
then be called upon to carry the same amount of current as 
was being carried in the remaining outside wire. For this 



-<v> ± 

_■ * B 

M ,^o 6 = >- 



Figure 85. 



reason the neutral wire must be of as great carrying capacity 
as the larger of the outside wires. 

The danger arising from the blowing of the neutral fuse 
(which this rule is designed to prevent) is .described under 
the next rule, 23 b. 

b. Must be placed at every point where a change is made 
in the size of wire [unless the cut-out in the larger wire will 
protect the smaller (See Table of Carrying Capacity)]. 

For three-wire direct current or single phase systems the 
fuse in the neutral wire except that called for under No. 23 d, 



CONSTANT-POTENTIAL SYSTEMS. 155 

may be omitted, provided the neutral wire is grounded as pro- 
vided for in No. 15. 

Figure 86, A to D, shows systems of distribution and ar- 
rangement of mains in general use. Figure A shows the 
simplest and cheapest method of running mains, and is known 
as the "tree system.'' Beginning at the service the wires 
must be large enough to carry the whole amount of current 
used to the first floor or wherever' the first cut-out center is 
located. At this point the size of wire may be reduced be- 
cause it will be required to carry only the current used further 
on. Main cut-outs should be arranged as shown in the figure 
at 1 and 2. That is, the cut-outs protecting the mains must 
be installed in the mains at each floor after the current for 
that floor has been taken off. Cases are often found where 
the cut-out is placed in the main line, ahead of the branch 
blocks. This is obviously wrong, as the fuse will have to be 
too heavy to protect the smaller mains. 

Figure B shows a somewhat different arrangement which 
requires more wire and is more expensive in the beginning, 
but far more satisfactory and economical in operation. With 
the wires arranged as shown in the diagram the pressure at 
all the lamps will be nearly uniform. Even if the mains are 
designed for a considerable loss to the center of distribution 
the dynamo may be made to compensate for this loss and 
keep the lamps burning properly. With the tree system, A, 
this is impossible ; the lamps at the first cut-out center will 
either be too bright or those at the last center too dim. 

Figure C shows a convertible three-wire system. 

In order to convert a three-wire system into a two-wire 
system the two outside wires are joined together. The mid- 
dle wire then forms one side of the system and the outside 
wires the other. The middle wire must carry as much cur- 
rent as both outside wires combined and should have a carry- 
ing capacity equal to them. It should be remembered that a 



156 



MODERN ELECTRICAL CONSTRUCTION. 




Figure 86. 



CONSTANT-POTENTIAL SYSTEMS. 1 57 

wire containing simply twice as many circular mils does not 
fulfill this requirement, as is shown in Table No. i on page 421, 
which must be consulted in selecting wires. 

In three-wire systems the middle or neutral wire is merely 
a balancing wire and normally carries very little or no cur- 
rent, but it is very important that it remain intact. If for in- 
stance in Figure D the branch circuit a has twelve lights 
burning while there are also twelve lights burning on b, the 
current will pass from the positive wire through the lower 
fuse to a, through the twelve lights in a back to the middle 
fuse, thence through the twelve lights in b to the upper fuse 
and negative wire, the two sets of lamps burning in series. 
If now the lamps in b are switched off the current from a can 
no longer pass through them and instead returns through the 
middle fuse to the neutral wire. If only six lights in b are 
burning, while twelve are burning in a, the current of six 
lights will return over the negative wire and the other six 
in a will return over the neutral wire. Should the neutral 
wire be broken or its fuse blown there would be no return 
path on it for the extra current, and consequently the cur- 
rent passing through the twelve lights in a would be forced 
to pass through the six lights in b, causing them to burn 
with excessive brilliancy and to break in a very short time. 
Should a short circuit occur, say on circuit b, with the neu- 
tral wire intact, it would merely blow out a fuse, but if the 
main neutral fuse were out it would bring 220 volts on cir- 
cuit a and speedily cause damage to the lamps. Thus it 
will be seen that it is of great importance to fuse the neutral 
wire so that it will not easily blow out. 

Figure C shows a system of wiring quite often used. A 
set of heavy mains are run from the service or dynamo to 
the top floor and taps taken off at each floor. These mains 
do not change size at each floor, but are continuous for. their 
entire length. While this method has some of the objections 



158 



MODERN ELECTRICAL CONSTRUCTION. 



of the tree system in regard to voltage, still the faults of the 
tree system are greatly reduced owing to the much smaller 
losses in the mains between the upper floors, or those farthest 



a 



TT 




& 



ff 



Figure 87. 



from the dynamo. Figure 87 shows a set of three-phase 
risers with branch circuit taps. 

Figure 88 shows the method of fusing main switch and 
bran:h circuits. The switch itself will require a fuse to pro- 
tect it, although it need not be right at the switch. 



CONSTANT-POTENTIAL SYSTEMS. 



159 



It often becomes necessary to reinforce a set of mains, 
especially for motors, which have become overloaded, by run- 
ning another wire in parallel with the old, as indicated in 
Figures 89 and 90. Two separate and distinct ways of ar- 
ranging them are shown and it depends upon the conditions 
as to which is preferable. If the wires are small or run in 
places where they are liable to be broken, the plan shown in 
Figure 89 is the better. Here each wire is properly fused and 
if one breaks the other carries the whole load until its fuse 
melts. If the wires, as often happens, are much overfused, 
the breaking of one wire would force the other to carry 
the whole current and become overheated. If the arrange- 




.— O HI O— l 

I r H>llo4 ] I 





Figure 88. 



Fig. 89. 



Fig. 90. 



Figure 91. 



ment were as in Figure 90 the unbroken wire would carry the 
current indefinitely and soon become overheated. On the 
other hand, if both wires are large and the run is short the 
fuses arranged as in Figure 89 may, through poor contacts, 
prevent one or the other of the wires from obtaining its 
full share of the current. The fuse making poor contact 
would force a much greater share of current through the 



i6o 



MODERN ELECTRICAL CONSTRUCTION. 



other wire. In most cases the better plan would be to ar- 
range the wires as in Figure 90. If the current supplied is 
for lights the branch cut-outs can be separated and each set 
of mains allowed to supply a certain part of them, when 
each set should be made independent. For sizes of wires to 
be used for reinforcing, see Tables. 

With the three-wire system where a large motor load 
and but few lights are used the lights are often fused as shown 




Figure 92. 



Figure 93. 



Figure 94. 



in Figure 91, a small wire being run for the neutral, this 
smaller wire, of course, being properly fused at the main cut- 
out. Plug cut-outs of the type shown in this figure often 
have the metal parts projecting above the porcelain; they 
should be connected so that the metal parts which project are 
dead when the plugs are removed. This will prevent many 
short circuits on disconnected cut-outs. 



CONSTANT-POTENTIAL SYSTEMS. 



161 



Figure 92 shows the method of converting a two-wire 
system into a three-wire system with one extra wire to run. 
This extra wire will very likely not need to be as large as the 
other wires are, because the three-wire system requires only 
one-half as much current and it should, therefore, be used as 
the neutral. This arrangement will secure the full benefit of 
all the copper in the old wires (which are probably much 
larger than necessary) and will operate at a very small loss. 

Figure 93 shows a straight three-wire system changed to 
a two-wire system, one extra wire run for it. If the three 
wires are of the proper capacity the addition of the fourth 
wire as in the figure will make it correct for two-wire sys- 
tems, the mains feeding the upper and lower groups being, of 
course, properly fused where they start. 

In Figure 94 the cut-outs are so connected that all branch 
wires leaving the cut-out box at either side are of the same 
polarity. This is often useful where many wires are to be 
run close together. 

Connections to three-phase systems are made as shown in 
Figures 95 and 96. 

Figure 95 shows the proper method of connecting plug 
cut-outs in "delta," and Figure 96 the connections for "star." 



1^1 




Figure 95 



The broken line indicates a balancing wire the office of which 
is somewhat similar to that of the neutral wire in a three-wire 
system. There are many cases in use where three-phase sys- 



1 62 



MODERN ELECTRICAL CONSTRUCTION. 



tems are connected in precisely the same manner as the ord' 
nary three-wire system but this is decidedly wrong although 
in certain cases it may work fairly well. 

c. Must be in plain sight, or enclosed in an approved 
cabinet, and readily accessible. They must not be placed in 
the canopies or shells of fixtures. 

Link fuses may be used only when mounted on approved 
slate or marble bases and must be enclosed in dust-tight, fire- 
proofed cabinets, except on switchboards. 

Edison plug cut-outs and enclosed cartridge fuses are not 
required by the rule to be enclosed in cabinets unless exposed 



1°^ 


— 






O () 


-o II i*- 





o 








' 


=8|llfc 


o 





r 


r> o 


=*U 18= 


-fr- 





1 


Figure 96. 


1 If U 1 


i 
1 

• 





to mechanical injury or close to easily ignitable material or 
where exposed to inflammable gases or dust or flyings of com- 
bustible material. Many cities, however, require the enclosing 
of these fuses and it is good practice to place all fuses in 
cabinets. 

Where this is not done the rule should be strictly en- 
forced as the older types of plug fuses with removable caps, 
and there are many still in use, become, with the cap removed, 
in reality open link fuses. Cartridge fuses are very frequently 
re-fused with fuse wire and the material from the inside of the 
fuse removed. They are also frequently re-fused with larger 
fuse wires than designed for and in numerous cases are found 
with fuse wire or other metal placed across the clips. 



CONSTANT-POTENTIAL SYSTEMS. 1 63 

While it is required that cut-out cabinets be accessible 
there is also danger in making them too accessible, for such 
cabinets are very often used for storage of paper or cotton 
waste. It would seem that about seven feet above the floor 
is the most desirable height to place them or the cabinet 
may be arranged with a slanting bottom which will make it 
impossible to store anything in it. It is also well to locate 
the cut-out cabinet away from inflammable material, for long 
experience has shown that doors are nearly always left open. 
Especially is this the case when switches are in the same 
cabinets with the cut-outs. 

d. Must be so placed that no set of incandescent lamps 
requiring more than 660 watts, whether grouped on one fixture 
or on several fixtures or pendants, will be dependent upon one 
cut-out. 

Special permission may be given in writing by the Inspec- 
tion Department having jurisdiction, for departure from this 
rule, in the case of large chandeliers. (For exceptions, see 
rule on theatre wiring.) All branches or taps from any three- 
wire system which are directly connected to lamp sockets or 
other translating devices, must be run as two-wire circuits if 
the fuses are omitted in the neutral, or if the difference of 
potential between the two outside wires is over 250 volts, and 
both wires of such branch or tap circuits must be protected 
by proper fuses. 

The above shall also apply to motors, except that small 
motors may be grouped under the protection of a single set 
of fuses, provided the rated capacity of the fuses does not 
exceed 6 amperes. 

The fuses in the branch cut-outs, except for motors as 
noted above, must not have a rated capacity greater than that 
given as follows for circuits at various potentials. 

55 volts or less 12 amperes 

Over 55 but less than 125 V. 6 amperes 

125 to 250 volts 3 amperes 

For sign and outline wiring supplied by circuits of 55 volts 
or less, branch circuit fuses of 25 ampere capacity may be 
used. 

On open work in large mills approved link fused rosettes 



1 64 MODERN ELECTRICAL CONSTRUCTION. 

may be used at a voltage of not over 125 and approved en- 
closed fused rosettes at a voltage of not over 250, the fuse in 
the rosettes not to exceed 3 amperes, and a fuse of over 25 
amperes must not be used in the branch circuit. 

The final circuit to which incandescent lamps are connected 
must never (except as noted) supply a greater load than 660 
watts. This limit has been determined by years of experience 
and it should never be exceeded. If a circuit is overfused, 
even though the wire supplying it may be of large carrying 
capacity, a short circuit in a piece of flexible cord or a brass 
shell socket may produce arc enough to cause a fire, and it 
must be remembered that a short circuit in a circuit protected 
by a six ampere fuse is much more severe where it occurs in 
a conductor of small capacity such as a flexible cord than it is 
in a conductor of greater capacity such as a No. 14 wire. 

The limit of the circuit being 660 watts some departments 
allow 13 lamps per circuit on the assumption that the ordinary 
16 candle power lamp requires only 50 watts. The more com- 
mon practice is to allow 12 lamps per circuit, figuring each 
lamp as taking 55 watts. 

The exception to the rule allow more lights on theater 
borders and large chandeliers. Theater borders are almost 
universally wired with either No. 14 or No. 12 standard wire 
and porcelain sockets so that a short is less liable to occur and 
is not so apt to result seriously. Large chandeliers, — such' as 
are used in churches, are never equipped with key sockets and 
all the lights on each circuit are switched on at one time. Un- 
der this condition the maximum current is always flowing 
through the fuses and but a slight excess is necessary to blow 
a fuse. The arc produced from a short is, therefore, much 
less destructive than in the case, for instance, of only one 
lamp burning on a circuit protected by a six ampere fuse. 

The rule allows three-wire branch circuits on systems 
where the neutral mains are fused and where the voltage does 



CONSTANT-POTENTIAL SYSTEMS. 165 

not execeed 250 volts. All other branch circuits must be two- 
wire and must have a fuse for each wire. Where three-wire 
branch circuits are used all three wires must be protected 
by fuses. 

Small motors may be grouped on one circuit if they do not 
require more than six amperes. Considerable discretion should 
be exercised in determining the number of motors to allow 
on one circuit under this rule as the starting current must be 
taken into consideration and not the normal current. It is 
difficult to specify the exact number of motors which may be 
allowed on a circuit under the rule as small motors have a 
very low and varying efficiency and, in the case of alternating 
current motors, sometimes take large starting currents. So- 
called 1/6 horse power motors will often blow a six ampere 
fuse. The safest procedure is to try out the motors under 
the condition of maximum load and if a six ampere fuse will 
hold them they will come within the rule. 

It will be noted that for systems of 55 volts or less not 
larger than 12 ampere fuses may be used on branch lighting 
circuits. Twenty-seven and one-half volt systems are used 
to some extent with tungsten lighting and the rule allows only 
330 watts on a circuit. This lower current limit is specified 
for general lighting circuits (exception is made for electric 
signs), to allow the use of the general class of fittings which 
are not made for large current capacities. 

e. The rated capacity of fuses must not exceed the al- 
lowable carrying capacity of the wire as given in No. 18. Cir- 
cuit-breakers must not be set more than 30 per cent above al- 
lowable carrying capacity of the wire, unless a fusible cut-out 
is also installed on the circuit. Where rubber-covered wire 
is used for the leads or branches of A. C. Motors of the types 
requiring large starting currents, the wire may be protected 
in accordance with Table B. of No. 18, except when circuit 
breakers are installed which are equipped with time element 
devices. 



1 66 MODERN ELECTRICAL CONSTRUCTION. 

Fixture wire or flexible cord of No. 18 B. & S. gage, will 
be considered as properly protected by 6 ampere fuses. 

Fuses are designed to blow at a current 25% in excess of 
their rated capacity (see 68 b and c). Circuit breakers are, 
therefore, allowed to be set at 30% over the allowable carry- 
ing capacity of the wire. If fuses of the proper size are pro- 
vided in the circuit, circuit breakers may be set at any point 
desired. 

For alternating current motors requiring large starting cur- 
rents the wires may be fused in accordance with the table of 
carrying capacity for "other insulations," this allowing an 
overfusing where rubber covered wire is used of about 50% 
for this class of service. 

A circuit breaker equipped with a time element device will 
allow a considerable overload to flow for a short period of 
time. After this time has elapsed the breaker will operate 
at the current for which it is set. 

/. Each wire of motor circuits, except on main switch- 
board or when otherwise subject to competent supervision, 
must be protected by an approved fuse whether automatic 
overload circuit breakers are installed or not. Single phase 
motors may have one side protected by an approved automatic 
overload circuit breaker only if the other side is protected by 
an approved fuse. For circuits having a maximum capacity 
greater than that for which enclosed fuses are approved cir- 
cuit breakers alone will be approved. 

The term "competent supervision" as applied to circuit 
breakers is often abused. A circuit breaker is so easily ad- 
justed that there is a great temptation to set them too high 
for proper protection and they should not be allowed to be 
used without fuses in the circuit unless the person who has the 
supervision of them thoroughly understands the possible re- 
sults which may follow their improper use. 



CONSTANT-POTENTIAL SYSTEMS. 167 

24. Switches. 

(See No. 19. For construction of Switches see No. 65.) 

a. Must be placed on all service wires, either overhead or 
underground, in the nearest readily accessible place, to the 
point where the wires enter the building, and arranged to cut 
off the entire current. 

Service cut-out and switch must be arranged to cut off 
current from all devices including meters. 

In risks having private plants the yard wires running from 
building to building are not considered as service wires, so 
that switches would not be required in each building if there 
are other switches conveniently located on the mains or if the 
generators are near at hand. 

In overhead construction the best plan is to locate the 
switch at either front or rear of building so that wires may 
lead to it direct from pole. Avoid running wires on sides 
of building where it is likely that other buildings may be 
erected. In underground construction, where the space under 
sidewalk and basement is not occupied, it is advisable to place 
a cut-out where wires enter the building from street and 
to locate the service switch in a more accessible place. 

Although the rules do not call for switch to be installed 
in each separate building in the case of large plants, still 
it is often advisable to install them, for in case of trouble 
it is necessary that the current can be immediately shut off. 
A switch is also useful in cases of trouble on the wiring, to 
allow of repairing. 

b. Must always be placed in dry, accessible places, and be 
grouped as far as possible. (See No. 19c.) Single-throw 
knife switches must be so placed that gravity will not tend to 
close them. Double-throw knife switches may be mounted so 
that the throw will be either vertical or horizontal as preferred. 

When practicable switches must be so wired that blades 
will be "dead" when switch is open. 

When switches are used in rooms where combustible fly- 



1 68 



MODERN ELECTRICAL CONSTRUCTION. 



ings would be likely to accumulate around them, they must 
be enclosed in dust-tight cabinets. 

Up to 250 volts and thirty amperes, approved indicating snap 
switches are suggested in preference to knife switches on lighting 
circuits. 

To comply with tliis rule will ordinarily bring the fuses 
of knife switches directly under the handle of switch. If 
there happens to be a short circuit on the wires when switch 
is closed the fuses will blow instantly and very likely burn 
the operator's hand. In connection with such switches car- 
tridge fuses should be used or the switches, especially the 




Figure 97. 



Figure 98. 



larger ones, closed by pushing them in with a stick. The 
danger from opening a switch is much less. 

Figure 97 shows a switch arranged to comply with all 
three points of this rule, the feed wires coming from below. 
This requires that incoming and outgoing wires pass each 
other. In this case, the wires pass each other behind the 
switch base, they being encased in flexible tubing. A side 
view is also given in Figure 98. Instead of passing behind 



CONSTANT-POTENTIAL SYSTEMS. 



l6g 



the switch the wires may, of course, run around one side to 
the top, the other wires around the other side to the bottom. 

Figure 98 illustrates a cabinet so arranged that the switch 
within can be opened or closed without opening the cabinet. 
The cover is hinged at the top, and slotted in the center, 
which leaves room for the lever by which the switch is 
worked to adjust itself so it will always be out of the way. 
A switch which is often used may as well be left without 
a cover as with one, for the door must be opened or closed 
every time the switch is used, and the cabinet will always 
be found open. Figure 98 will answer where only protection 
against accidental contacts is required. 

c. Single pole switches must never be used as service 
switches nor for the control of outdoor signs nor placed in 
the neutral wire of a three-wire system, except in the two-wire 
branch or tap circuit supplying not more than 660 watts. 

This, of course, does not apply to the grounded circuits 
of Street Railway systems. 

Three-way switches are considered as single pole switches. 

This rule allows the use of single pole switches (except 
for service switches and the control of outdoor signs) on cir- 




Figure 99. 



cuits of 660 watts, 6 amperes at no volts, or 3 amperes at 220 
volts, which corresponds roughly to twelve 16 c. p. lamps. 
In systems that are not grounded a single pole switch 'will 
answer fairly well if large enough. It will readily open the 



170 MODERN ELECTRICAL CONSTRUCTION, 

circuit and it offers no opportunities for short circuits, as do 
double pole switches. Where, however, three-wire systems 
with grounded neutrals are used double-pole switches are 
preferable, for by reference to Figure 99 one can readily see 
that if the neutral or middle wire is grounded (which is 
equivalent to being in connection with gas piping) and an- 
other ground should come onto the wiring say at a, the single- 
switch, S, would not control the lights at all. The current 
would flow from the positive wire to the top fuse, through the 
twelve lights to ground a, through the ground to the neu- 
tral or middle wire and back to the dynamo, regardless of 
whether the switch is on or off. Also, a man working at the 
lights could easily make a short circuit by bringing the wires 
into contact with the gas piping even if the switch were turned 
off. When single-pole switches are used in connection with 
such circuits it is inadvisable to place them in the neutral 
wires as shown in the figure. If single-pole switch was placed 
in the upper wire in Figure 99 these troubles would be avoided. 
It is however often impracticable, in ordinary construction 
work to place single-pole switches in the outside wires, be- 
cause these cannot be determined before connection and for 
this reason the requirement is waived. Where the time can 
be given it is always much better to avoid switches in the neu- 
tral wire and with some of the wires now on the market, 
where one wire of each duplex wire is marked it is an easy 
matter to accomplish this. 

Three-way switches must not be used on circuits of over 
660 watts. In wiring up three-way switches if both poles 
of the circuit are brought to the switch only one wire need 
be run between the switches, but where both poles of the 
circuit are connected into the switch the arc produced on 
operating the switch may carry from one pole to the other 
and cause a short circuit. 

For full and comprehensive description of "three-way" 



CONSTANT-POTENTIAL SYSTEMS. \Jl 

switches the reader is referred to "Modern Wiring Diagrams 
and Descriptions" by the authors of this work. 

d. Where flush switches or receptacles are used, whether 
with conduit systems or not, they must be enclosed in an ap- 
proved box constructed of iron or steel, in addition to the 
porcelain enclosure of the switch or receptacle. No push but- 
tons for bells, gas-lighting circuits, or the like shall be placed 
in the same wall plate with switches controlling electric light 
or power wiring. 

Steel boxes designed to hold either a flush switch or a re- 
ceptacle are made for this purpose. They are provided with 
holes into which the wire which is protected by flexible tub- 
ing may be carried. This requirement is necessary as the por- 
celains may be broken either in installing or afterward and, 
of course, in this condition would present a hazard unless en- 
cased in a fireproof enclosure such as the steel box demanded. 

As there is always a liability of the face plate or enclosing 
box surrounding switches becoming alive from contact with 
the lighting wires no push button controlling bells or gas light- 
ing circuits should ever be placed on the same wall plate 
with them, for under such conditions the lighting current could 
be carried on the bell wires. With gas lighting systems high 
tension sparks are sometimes used for the ignition of the 
gas and with the wires carrying this current on the same wall 
plate with lighting switches there would be a tendency for the 
high tension current to jump to the lighting circuit and cause 
grounds or short circuits. 

e. Where possible, at all switch or fixture outlets, unless 
outlet boxes which will give proper support for fixtures are 
used, a seven-eighths inch block must be fastened between 
studs or floor timbers flush with the back of lathing to hold 
tubing, and to support switches or fixtures. When this cannot 
be done, wooden base blocks, not less than three-fourths inch 
in thickness, securely screwed to lathing, must be provided 



172 



MODERN ELECTRICAL CONSTRUCTION. 



for switches, and also for fixtures which are not attached to 
gas pipes or conduit. 

Figure ioo shows concealed wiring back of lathing leading 
to a double-pole flush switch. The board fastened between 
studdings must be cut out to admit the box of switch and 
the size of this box should be known when wires are put in. 
The board should not rest hard against the lathing, but 
leave a little space for plaster to work in behind the lath. 






IT 



Figure 100. 



Figure 101. 



Loom is put on all wires at outlets and must extend back 
to the nearest knob. 

Figure ioi shows two methods of fastening snap switches 
by means of wooden blocks first fastened to the plaster. One 
block is cut out so as to bring all wires under the switch 
and entirely conceal them. The opening in block to admit 
wires and bushings should be oblong, so as to leave room 
on two sides for the screws with which the switch is to be 
fastened. On the other block the wires and bushing are 
brought through close to the outer edge of switch base. 
By careful workmanship a neat job can be done in this way. 
As most snap switches cross conductors, that is, connect 



CONSTANT-POTENTIAL SYSTEMS. 1 73 

points a and b, if from the nature of the case it becomes 
necessary to run any of the wires close together these two 
wires may be run that way, for they can never be of oppo- 
site polarity. 

f. Sub-bases of non-combustible, non-absorptive, insulat- 
ing material, which will separate the wires at least one-half 
inch from the surface wired over, must be installed under 
all snap switches used in exposed knob and cleat work. Sub- 
bases must also be used in moulding work, but they may be 
made of hardwood or they may be omitted if the switch is ap- 
proved for mounting directly on the moulding. 

25. Electric Heaters. 

It is often desirable to connect in multiple with the heaters 
and between the heater and the switch controlling same an in- 
candescent lamp of low candle power, as it shows at a glance 
whether or not the switch is open and tends to prevent its being 
left closed through oversight. 

a. Must be protected by a cut-out and controlled by in- 
dicating switches. Switches must be double pole except when 
the device controlled does not require more than 660 watts 
of energy. 

b. Must never be concealed, but must at all times be in 
plain sight. 

Special permission may be given in writing by the Inspec- 
tion Department having jurisdiction for departure from this 
rule. 

c. Flexible conductors for smoothing irons and sad irons, 
and for all devices requiring over 250 watts must have an ap- 
proved insulation and covering. 

d. For portable heating devices the flexible conductors 
must be connected to an approved plug device, so arranged 
that the plug will pull out and open the circuit in case any 
abnormal strain is put on the flexible conductor. This device 
may be stationary, or it may be placed in the cord itself. The 
cable or cord must be attached to the heating apparatus in 
such manner that it will be protected from kinking, chafing 
or like injury at or near the point of connection. 

e. Smoothing irons, sad irons, and other heating appli- 
ances that are intended to be applied to inflammable articles, 
such as clothing, must conform to the above rules so far as 
they apply. They must also be provided with an approved 
stand, on which they should be placed when not in use. 



174 



MODERN ELECTRICAL CONSTRUCTION. 



f. Stationary electric heating apparatus, such as radiators, 
ranges, plate warmers, etc., must be placed in a safe location, 
isolated from inflammable materials, and be treated as sources 
of heat. 

Devices of this description will often require a suitable heat- 
resisting material placed between the device and its surroundings. 
Such protection may best be secured by installing two or more 
plates of tin or sheet steel with a one-inch air space between or 
by alternate layers of sheet steel and asbestos with a similar air 
space. 

•g. Must each be provided with name-plate, giving the 

maker's name and the normal capacity in volts and amperes. 




Figure 102. 

In Figure 102 is given a diagram of a heater circuit with 
a 4 c. p. lamp in circuit. Where there are many irons in use, 
as in some tailoring establishments, it is advisable to run 
them all from one set of mains with a main switch conveni- 
ent to exit door and have this switch opened whenever the 
irons are not in use. The individual switch at each iron 
should be located as near as possible to each iron. Cords 
feeding irons or cloth cutting machines are often installed 
as shown, insulators are strung on a tight wire and the cord 
tied to them. This allows considerable latitude in moving 
the iron. 



LOW-POTENTIAL SYSTEMS. 

550 Volts or Less. 

Any circuit attached to any machine, or combination of ma- 
chines, which develops a difference of potential between 
any two wires, of over ten volts and less than 550 volts, 
shall be considered as a low-potential circuit, and as coming 
under this class, unless an approved transforming device is 
used, which cuts the difference of potential down to ten 
volts or less. The primary circuit not to exceed a poten- 
tial of 3,500 volts, unless the primary wires are installed 
in accordance with the requirements as given in No. 13, or 
are underground. For 550 volt motor equipments a mar- 
gin of ten per cent above the 550 volt limit will be allowed 
at the generator or transformer. 

26. Wires. 

GENERAL RULES. 

(See also Nos. 16, 17 , 18 and 27. For construction rules see 

Nos. 49 to 57.) 

a. Where entering cabinetes must be protected by ap- 
proved bushings, which fit tightly the holes in the box and are 
well secured in place. The wires should completely fill the 
holes in the bushings so as to keep out the dust, tape being 
used to build up the wires if necessary. On concealed knob 
and tube work approved flexible tubing will be accepted in 
lieu of bushings, providing it shall extend from the last por- 
celain support into the cabinet. 

b. Must not be laid in plaster, cement or similar finish, 
and must never be fastened with staples. 

c. Must not be fished for any great distance, and only in 
places where the inspector can satisfy himself that the rules 
have been complied with. 

Figure 103 illustrates a very common combination of "fish" 

and "moulding" work. Moulding is used to bring the wires 



176 



MODERN ELECTRICAL CONSTRUCTION. 



from the floor to the ceiling and along the ceiling to a point 
opposite the outlet and parallel with the joists. From this 
point to the fixture the wires can then be readily fished. 

The connection between the fish and moulding work should 
be made as shown at the right, where the moulding is cut 



^ \ \ \ \ \ \ \ i i 




Figure 103. 



out so as to admit the loom. It is better, even, to have the 
loom show to some extent than to have the wire come in 
contact with the plaster, as will very likely be the case if the 
loom is not fully brought through. 

d. Twin wires must never be used, except in conduits, or 
where flexible conductors are necessary. 



LOW-POTENTIAL SYSTEMS. 



177 



Flexible conductors are in general considered necessary 
only with pendant sockets, certain styles of adjustable brack- 
ets, portable lamps, motors and stage plugs, or heating ap- 
paratus. 

e. Must where exposed to mechanical injury be suitably 
protected. When crossing floor timbers in cellars, or in rooms 
where they might be exposed to injury, wires must be at- 
tached by their insulating supports to the under side of a 
wooden strip, not less than one-half inch in thickness, and 
not less than three inches in width. Instead of the running 
boards, guard strips on each side of and close to the wires 
will be accepted. These strips to be not less than seven- 
eighths of an inch in thickness and at least as high as the 
insulators. 

Protection on side walls must extend not less than five 
feet from the floor and must consist of substantial boxing, 



■^\^<\^V\\\v\\\\\\\\\A\u\\\M \ . 1 1 1 1 ,nr U ! / ill t ' ///y//^////////// 




w^mmm^m 



Figure 104. 

retaining an air space of one inch around the conductors, 
closed at the top (the wires passing through bushed holes) 
or approved metal conduit or pipe of equivalent strength. 

_ When metal conduit or pipe is used, the insulation of each 
wire must be reinforced by approved flexible tubing extending 
from the insulator next below the pipe to the one next above 
it, unless the conduit is installed according to No. 28 (Sections 
c and f excepted), and the wire is approved for conduit use. 
The two or more wires of a circuit each with its flexible tub- 



178 



MODERN ELECTRICAL CONSTRUCTION. 



ing (when required), if carrying alternating current must, or 
if direct current, may be placed within the same pipe. 

In damp places the wooden boxing may be preferable because 
of the precautions which would be necessary to secure proper in- 
sulation if the pipe were used. With this exception, however, iron 
piping is considered preferable to the wooden boxing, and its use 
is strongly urged. It is especially suitable for the protection of 
wires near belts, pulleys, etc. 

Figure 104 illustrates the meaning of the rule in regard 
to wires run along low ceilings. 

Figure 105 gives the dimensions necessary for the box- 
ing surrounding wires on side walls. The figure also show? 




Figure 105. 



the method of running wires in common iron pipe such as 
steam pipe. In this case the wires are each protected by an 
additional covering of flexible tubing. At the right of the fig- 



LOW-POTENTIAL SYSTEMS. 179 

ure is shown the more common method of using conduit for 
the protection of the wires. Approved conduit with outlet 
fittings at each end is securely fastened in place. Double 
braid, rubber covered wire, such as is required for conduit 
work must be used. The sections of the rule governing con- 
duit work which do not apply in this case are : the wire may 
be pulled in before the mechanical work on the building is 
completed, and, it is not necessary to ground the conduit. This 
method of protecting wires is very satisfactory and is often 
used around belts and around machinery. Where the con- 
ditions are such as to require protection in a number of places 
it is often better to use single wires, each with a double braid, 
as this will do away with the necessity of splicing short lengths 
of double braid wire where passing through the short lengths 
of conduit. 

f. When run in unfinished attics, will be considered as 
concealed, and when run in close proximity to water tanks or 
pipes, will be considered as exposed to moisture. 

In unfinished attics, wires are considered as exposed to me- 
chanical injury, and must not be run on knobs on upper edge 
of joists. 

The question sometimes arises as to what is an "unfin- 
ished attic." In general an attic may be considered as un- 
finished when it is not provided with a floor and also with a 
permanent stairway leading to it. Attics are generally used 
for the storage of various household articles and where wires 
are run on tops of joists they are very liable to be injured. 
They should be run on the side of the joists and through bush- 
ings when running crosswise of the joists. 

SPECIAL RULES. 

For Open Work. 
In dry places. 

g. Must have an approved rubber, slow-burning weather- 
proof, or slow-burning insulation. 



l80 MODERN ELECTRICAL CONSTRUCTION. 

A slow-burning covering, that is, one that will not carry fire, 
is considered good enough where the wires are entirely on insulat- 
ing supports. Its main object is to prevent the copper conductors 
from coming accidentally into contact with each other or any- 
thing else. 

h. Must be rigidly supported on non-combustible, non- 
absorptive insulators, which will separate the wires from each 
other and from the surface wired over in accordance with the 
following table: 

Distance from Distance between 
Voltage. Surface Wires. 



to 300 


y 2 inch 


2V 2 inch 


300 to 550 


1 inch 


4« inch 



Rigid supporting requires under ordinary conditions, where 
wiring along flat surfaces, supports at least every four and 
one-half feet. If the wires are liable to be disturbed, the dis- 
tance between supports must be shortened. In buildings of 
mill construction, mains of not less than No. 8 B. & S. gage, 
where not liable to be disturbed, may be separated about six 
inches, and run from timber to timber, not breaking around, 
and may be supported at each timber only. 

The neutral of a three-wire system may be placed in the 
center of a three-wire cleat where the difference of potential 
between the outside wires is not over 300 volts, provided the 
outside wires are separated two and one-half inches. 

Must not be "dead-ended" at a rosette socket or receptacle 
unless the last support is within twelve inches of the same. 

Rubber covered wire is ordinarily used for open work al- 
though slow-burning weatherproof wire or slow-burning wire 
may be used. The slow-burning weatherproof wire has an 
inner coating of weatherproof material of the same character 
as on outside weatherproof wire. Outside of the coating is 
placed a coating, fireproof in character, and similar to the cov- 
ering on the so-called "underwriters" wire. The purpose of 
this covering is to provide an insulation which will protect the 
wires under ordinary circumstances. It is not suitable where 
moisture is present. The inner coating affords a fairly good 
insulating covering and the outer coating a protection against 
fire. 



LOW-POTENTIAL SYSTEMS. 



181 



The slow-burning wire has a covering specially designed to 
withstand heat or fire and is only used in very hot places or 
where a number of wires are bunched. It is also used where 
gases or fumes are present which would have a tendency to 
destroy the rubber of the rubber-covered wire. 

Figure 106 shows a number of methods of running wires in 
buildings of mill* construction. At a the wires are carried 





ff 




4d- 



Figure 106. 



drj- 



through bushings through the beams and supported between 
beams on porcelain insulators. As beams in buildings of mill 
construction are generally quite thick, the installation of bush- 
ings is expensive and one of the other methods is generally 
used. The method shown at b is very frequently used. If the 
beams are not too thick the wires may be run as shown at c. 
If the wire is large and the ceiling is high so that wires are 



l82 MODERN ELECTRICAL CONSTRUCTION. 

not liable to be disturbed they may be run as shown at d. 
With long spans an insulator may be placed on the wire and 
supported as shown at e. 

In damp places, or buildings specially subject to moisture or 
to acid or other fumes liable to injure the mires or their 
insulation. 

i. Must have an approved insulating covering. 

For protection against water, rubber insulation must be 
used. For protection against corrosive vapors, either weather- 
proof or rubber insulation must be used. 

/. Must be rigidly supported on non-combustible, non- 
absorptive insulators, which separate the wire at least one 
inch from the surface wired over, and must be kept apart at 
least two and one-half inches for voltages up to 300, and four 
inches for higher voltages. 

Rigid supporting requires under ordinary conditions, where 
wiring over flat surfaces, supports at least every four and 
one-half feet. If the wires are liable to be disturbed, the dis- 
tance between supports must be shortened. In buildings of 
mill construction, mains of not less than No. 8 B. & S. gage, 
where not liable to be disturbed, may be separated about six 
inches, and run from timber to timber, not breaking around, 
and may be supported at each timber only. 

In damp places wires are often run on the under side of an 
inverted trough as shown in Figure 107. The main point of 
usefulness of such a trough lies in the fact that it prevents 
drippings from wetting the wires and insulators. Condensa- 
tion will, however, keep insulators and wires wet. 

The trough to be useful should be put together with many 
screws or nails, the butting edges of the boards having been 
first painted with a waterproof paint, with which, wrien fin- 
ished, the whole trough is also painted inside and out. If nails 
are used it will be found that cut iron nails are much less liable 
to corrosion than the ordinary wire nail. The trough should 
be made deep enough to protect the wires and should be hung 



LOW-POTENTIAL SYSTEMS. 183 

as low as practicable so as to bring the wires into an even 
temperature. This construction will also avoid long drops or 
cords. 

In connection with wiring in wet places, it is well to re- 
member that a stranded wire is much more liable to corrosion 
than a solid wire, for, when exposed, the smaller wires of the 
strand provide a greater exposed surface than the equivalent 
solid wire. The space between the wires of a strand is very 





Figure 107. 

liable to become full of water due to the capillary attraction of 
the small wires of the strand. With the trough method of 
construction the drops may be suspended from a split knob. 

It is not practical to give exact rules covering electrical 
construction in all kinds of wet places or in locations exposed 
to acid fumes as the conditions vary greatly. Constant experi- 
ments are being carried on to determine the best class of con- 
struction for each particular class of service and the Inspection 
Department having jurisdiction should be consulted in each 
^ase before starting any work. It is found at the present time 
that in some locations it is necessary to change the wiring 
every year. 



184 MODERN ELECTRICAL CONSTRUCTION. 

Each insulator when wet allows some current to leak over 
its surface and, therefore, the fewer we have the better the 
construction so long as there is no danger of the wires break- 
ing. A form of construction which has given good service 
where others have failed consists of wires supported on petti- 
coat insulators with the insulators some distance apart. It 
may be necessary to use a somewhat larger wire than ordi- 
narily but the reduction in the losses from leakage and the 
trouble from grounds will more than repay the added expense. 
A modification of this construction consists in running wires 
on split knobs placed some distance apart with strain insulators 
at each end of the wire to take care of the strain. 

If splices are necessary in wet places they should be made 
some distance away from the insulators, the insulation at the 
splice being always weaker than that of the unbroken wire. 
Care should always be taken that the insulation is not dam- 
aged by tying or by clamping under split knobs. 

Weather proof sockets are required by the rule. Porce- 
lain weatherproof sockets where exposed to changes in tem- 
perature will often crack and fall apart. In such places the 
moulded composition sockets are better. Brass shell sockets 
with the butt of the lamp and the entire socket taped and then 
compounded, while not in accordance with the rule, have 
proven very durable. In all cases whether the lamp is being 
used or not it should be left in the socket as it will tend to 
preserve the inner contacts of the socket. 

When clusters are used the supporting stem should be left 
open at the bottom so that no accumulation of moisture can- 
gather inside the stem. This construction will also allow a cir- 
culation of air which will tend to keep the wires inside the 
stem dry. 



LOW-POTENTIAL SYSTEMS. 185 

For Moulding Work (Wooden and Metal). 

(See No. 29. For construction of Mouldings see No. 60.) 

k. Must have an approved rubber insulating covering, 
and must be in continuous lengths from outlet to outlet, or 
from fitting to fitting, no joints or taps to be made in mould- 
ing. Where branch taps are necessary in moulding work 
approved fittings for this purpose must be used. 

/. Must never be placed in either metal or wooden mould- 
ing in concealed or damp places, or where the difference of 
potential between any two wires in the same moulding is over 
300 volts. Metal mouldings must not be used for circuits re- 
quiring more than 660 watts of energy. 

m. Must for alternating current systems if in metal 
moulding have the two or more wires of a circuit installed 
in the same moulding. 

It is suggested tbat this be done for direct current systems, also 
so that they may be changed to alternating systems at any time, 
induction troubles preventing such a change if the wires are in 
separate mouldings. 

Figure 108 shows the dimensions of approved moulding. 
Wires in moulding should always be approved rubber cov- 
ered. Slow burning weatherproof wire, such as is allowed in 




Figure 108. 

some classes of open work, should never be used in moulding. 
For use in metal moulding single braid rubber covered wire 
is approved. 

The rules covering moulding work in previous years al- 
lowed joints in the wire within the moulding. This is now 
forbidden for various reasons among which are the following: 
It is almost impossible to place a properly insulated joint in 
moulding as it is generally found necessary to cut away the 



i86 



MODERN ELECTRICAL CONSTRUCTION. 



tongue between the wires. There was a great tendency to 
leave joints unsoldered and in many cases untaped for, be- 
ing covered, they could not be discovered without removing 
the capping. An overheated joint was almost sure to cause a 




Figure 109. 

fire. In making taps wires were often crossed under the 
capping. 

The present construction demands the use of fittings for all 
branch taps, all receptacles and all drops. Fittings designed 
to be used for the purposes specified are shown in Figure 109. 




Figure no shows how moulding should be fastened to tile 
ceiling. When toggle bolts are used, the nut should always be 
put on outside of capping (unless a very small one is used, or 
more than ordinary care is exercised). Many wiremen are 



LOW-POTENTIAL SYSTEMS. 



I8 7 



careless and cut away the middle tongue too much, giving the 
nut a chance to work itself diagonally across it, so as to come 
in contact with both wires and, in time perhaps, cause short 
circuits. Although toggle bolts are mostly used, screws have 




Figure 111. 

been successfully used in tile. It is only necessary to first 
drill a hole of just the proper size for the screw to be used. 
The proper way of making a square turn in moulding is 




Figure 112. 



shown in Figure III. It will be noted that the sharp ends of 
the moulding are cut away at the turns. 

Figure 112 shows methods of running around corners. 
The saw cuts, a, b, c, etc., should be made with a fine saw and 
for short bends require to be close together. Bending is 
facilitated by wetting the moulding, and if, before the mould- 



188 MODERN ELECTRICAL CONSTRUCTION. 

ing is put in place, the saw cuts are filled with glue, it will 
greatly add to the durability of the job. Screws or nails 
used in fastening the capping should pass through the mould- 
ing into the wall to get a firm hold. 

For Conduit Work. 

n. Must have an approved rubber insulating covering, 
and must within the conduit tubing be without splices or 
taps. 

o. Must not be drawn in until all mechanical work on the 
building has been, as far as possible, completed. 

Conductors in vertical conduit risers must be supported 
within the conduit system in accordance with the following 
table :— 

No. 14 to o every 100 feet. 

No. 00 to 0000 every 80 feet. 

°ooo to 350,000 C. M. every 60 feet. 

350,000 C. M. to 500,000 C. M. every 50 feet. 

500,000 C. M. to 750,000 C. M. every 40 feet. 

750,000 C. M. every 35 feet. 

The following methods of supporting cables are recom- 
mended : — 

1. A turn of 90 degrees in the conduit system will con- 

stitute a satisfactory support. 

2. Junction boxes may be inserted in the conduit sys- 

tem at the required intervals, in which insulating 
supports of approved type must be installed and se- 
cured in a satisfactory manner so as to withstand 
the weight of the conductors attached thereto, the 
boxes to be provided with proper covers. 

3. Cables may be supported in approved junction boxes 

on two or more insulating supports so placed that 
the conductors will be deflected at an angle of not 
less than 90 degrees, and carried a distance of not 
less than twice the diameter of the cable from its 
vertical position. Cables so suspended may be ad- 
ditionally secured to these insulators by tie wires. 
Other methods, if used, must be aprpoved by the Inspec- 
tion Departments having jurisdiction. 



LOW-POTENTIAL SYSTEMS. l8g 

p. Must, for alternating systems, have the two or more 
wires of a circuit drawn in the same conduit. 

It is suggested that this be done for direct current systems also 
so that they may be changed to alternating systems at any time, 
induction troubles preventing such a change if the wires are in 
separate conduits. 

The same conduit must not contain more than four two- 
wire, or three three-wire circuits of the same system, except 
by special permission of the Inspection Department having 
jurisdiction, and must never contain circuits of different 
systems. 

Rubber covered wire only may be used in conduit. For 
conduit with a lining of insulated material single braid wire 
may be used. For unlined conduit the wire must have two 
braids or one tape and a braid. The two braids are preferable 
for twin or duplex wires for the reason that where the outer 
braid of the duplex wire is removed as at switch and fixture 
outlets tape is apt to unwind and leave the wire with a rubber 
covering only. With the duplex wire having braids on each 
wire the single wires will still be protected by braids. Rule o 
is required to insure the protection of the wiring from me- 
chanics working on the building. It also insures that there 
will be no runs installed in which the wire cannot be at any 
time inserted. Where the wire is pulled into the conduits be- 
fore the mechanical work is entirely finished there is a tempta- 
tion to open long conduit runs at the middle and pull the wires 
both ways. Obviously, it will be a difficult matter to replace 
such runs should they burn out. 

Figure 113 shows different methods employed to fasten 
wires in vertical runs in conduits. In the upper left-hand 
figure insulators are used, reinforced by metal straps so ar- 
ranged that they will prevent the insulators from being pulled 
off sideways. The method shown in the lower figure is some- 
times used with cables so heavy that the rubber insulation 
will not stand the strain of supporting them. The figure 
shows a clamp made of copper so that it can be soldered to 



190 



MODERN ELECTRICAL CONSTRUCTION. 



the baie wires of the cable. This clamp is mounted on slate 
so as to furnish the insulation necessary for the cable. 

If a single wire carrying alternating currents of electricity 
were run in iron pipe there would be a very large drop in 



G* 




■ w 




• '.3— N 


-*fe 


fj/€> 






<4^| 


^-4 





u 



J^. 






jA. 







Figure 113. 



voltage. This drop is due to the fact that all currents while 
changing in strength generate a counter E. M. F. in their sur- 
roundings. This is particularly strong when the wires are sur- 
rounded by, or very close to, iron. If both wires are run in 
the same pipe the current in one wire neutralizes that of the 
other and there is no trouble. 



LOW-POTENTIAL SYSTEMS. 



1 90 A 



Figure 113A and the tabulation given below are designed to 
assist in laying out conduit runs where turns are to be made 
or where there are obstructions as in mill-constructed build- 
ings. In the column at the left are given. various radii of bends. 
In column 1 is skown the saving in length of conduit' effected 
by making single bends of different radius over what would 
be required to make square turns. 




Fig. 113A. 



To find the actual length of conduit required, measure the 
run as though it were made square and subtract the length 
in inches set opposite the corresponding radius of bend. If 
the bend is made a true circle the radius will be equal to the 
distance from beginning of bend to where the conduit strikes 
the ceiling. 

Where it is necessary to run around a beam as shown in 
column 2 and the same radius of bend is used there will be 
four bends and the saving will be four times as great as for 
the single bend, but it must be borne in mind that a four-inch 
radius, for instance, cannot be used unless the beam is at least 
eight inches high. 

In many cases the run around a beam is made about as in- 
dicated in column 3. The saving effected by this manner 
of bending is approximately given in column 3. 





1 


2 




3 


Radii 


Saving 


Saving 


Height 


Saving 


of bends, 


in conduit, 


in conduit, 


of beam, 


in conduit, 


inches 


inches 


inches 


inches 


inches 


3 


It 6 * 


sy 4 


1 


% 


4 


1% 


7 


2 


1 


5 


2Ys 


8 V2 


3 


11/2 


6 


2% 


10 y 2 


4 


2 


7 


3 


12 


5 


21/2 


8 


3 T 7 s 


13% 


6 


3 


9 


3% 


15V2 


7 


31/2 


10 


4ft 


17 y 4 


8 


4 


11 


4% 


19 


9 


4y 2 


12 


sA 


20% 


10 


5 


13 


5% 


221/2 


11 


51/2 


14 


6 T V 


241/4 


12 


6 



190B 



MODERN ELECTRICAL CONSTRUCTION. 



The following tables show the number of wires of various 
sizes which are allowed in conduit. These tables appear in the 
1915 edition of the National Electrical Code. In this same edi- 
tion the rules governing the construction of rubber-covered 
wire were changed to allow all wires up to and including No. 
8 B. & S. gauge to have a single-braid covering. This change 
in the rule was not taken into account in compiling the tables 
given in the National Electrical Code and due to the fact that 
the single-braid covering is somewhat smaller than the pre- 
viously required double-braid covering, many cities are permit- 
ting more wires in a conduit than those shown in the tables, 
which appear in the National Electric Code. Tables have, 
therefore, been added showing combination using single-braid 
wires in conduit. 



3 Conductor Convertible System 



Size of conductors 


Size Conduit, in. 


2-conductor 


1-conductor 


Electrical trade 


Size B. & S. 


Size B. & S. 


size 


14 


10 


% 


12 


8 


% 


10 


6 


1 


8 


4 


1 


6 


2 


1% 


5 


1 


1% 


4 





1% 


3 


00 


W 


2 


000 


1 


0000 


2 





250000 


2 


00 


350000 


2y 2 


000 


400000 


2% 


0000 


550000 


3 


250000 


600000 


3 


300000 


800000 


3 


400000 


1000000 


31/2 


500000 


1250000 


4 


600000 


1500000 


4 


700000 


1750000 


41/2 


800000 


2000000 


4V 2 



LOW-POTENTIAL SYSTEMS. 



IQOC 



Size of Conduits for the Installation of Wires and Cables 





One 


Two 


Three 


Four 




conductor 


conductors 


conductors 


conductors 




in a 


in a 


in a 


in a 




conduit 


conduit 


conduit 


conduit 




Electrical 


Electrical 


Electrical 


Electrical 


Size 


• trade 


trade 


trade 


trade 


B. & S. 


size 


size 


size 


size 


*14 


V> 


V2 


V2 


% 


*12 


V2 


% 


% 


% 


*10 


V2 


% 


% 


1 


* 8 


V2 


1 


1 


1 


6 


¥2 


1 


1% 


iy* 


5 


% 


1V4 


1V4 


iy* 


4 


% 


IV4 


1V4 


iy 2 


3 


% 


lVi 


1% 


1% 


2 


% 


1% 


1V2 


iy 2 


1 


% 


IV2 


1% 


2 





1 


1% 


2 


2 


00 


1 


2 


2 


2y 2 


000 


1 


2 


2 


2% 


0000 


1M 


2 


2V 2 


2% 


CM 










200000 


1% 


2 


2y 2 


2y 2 


250000 


iy 4 


2V 2 


2v 2 


3 


300000 


1% 


2y 2 


21/2 


3 


400000 


1V4 


3 


3 


3y 2 


500000 


1% 


3 


3 


3y a 


600000 


1% 


3 


3y 2 




700000 


2 


31/2 


31/2 




800000 


2 


3V 2 


4 




900000 


2 


3V2 


4 




1000000 


2 


4 


4 




1250000 


21/2 


4V 2 


41/2 




1500000 


2% 


41/2 


5 




1750000 


3 


5 


5 




2000000 


3 


5 


6 





♦Single Conductor, Single Braid, Solid Wires Only 

(This table is not to be used for double braid wires, twin or 
duplex wires or stranded wires.) 



14 


y 2 


y 2 


y 2 


y 2 


12 


% 


y 2 


% 


% 


10 


y 2 


% 


% 


1 


8 


y 2 


% 


% 


1 



190D 



MODERN ELECTRICAL CONSTRUCTION. 



Size of Conduit for the Installation of Wires. 
Twin Conductor. 





One 

conductor 

in a 

conduit 


Two 

conductors 

in a 

conduit 


I 

Three 

conductors 

in a 

conduit 


Four 

conductors 

in a 

conduit 


Size 
B. &S. 


Electrical 

trade 

size 


Electrical 

trade 

size 


Electrical 

trade 

size 


Electrical 

trade 

size 


14 
12 
10 


y 2 

y 2 


% 
% 
1 


1 
1 

1V4 


1 

1V4 
1V 4 



Combinations Where Double Braid, Twin or Duplex W T ires Are Used 

Size conduit, in. 
No. of Electrical 

Wires trade size 

*5 No. 14 R. C. solid % 

*10 No. 14 R. C. solid 1 



Where special permission has been given in accordance with No. 
26, p, the following table to apply : 

18 No. 14 R. C. solid 1 V± 

24 No. 14 R. C. solid IV2 

40 No. 14 R. C. solid 2 

74 No. 14 R. C. solid 2V 2 

90 No. 14 R. C. solid 3 



* Combinations W T here Single Conductor, Single Braid, Solid Wires 

Are Used. 

(This table is not to be used for double braid wires, twin or 
duplex wires.) 

Size conduit, in. 
No. of Electrical 

Wires trade size 

7 No. 14 R. C, solid % 

12 No. 14 R. C. solid 1 



LOW-POTENTIAL SYSTEMS. I9I 

For Concealed "Knob and Tube" Work. 

q. Must have an approved rubber insulating covering. 

r. Must be rigidly supported on non-combustible, non- 
absorptive insulators which separate the wire at least one inch 
from the surface wired over. Should preferably be run singly 
on separate timbers, or studding, and must be kept at least 
five inches apart. 

Must be separated from contact with the walls, floor tim- 
bers and partitions through which they may pass by non-com- 
bustible, non-absorptive, insulating tubes, such as glass or por- 
celain. Wires passing through cross timbers in plastered par- 
titions must be protected by an additional tube extending at 
least four inches above the timber. 

Rigid supporting requires, under ordinary conditions, where 
wiring along flat surface, supports at least every four and one- 
half feet. If the wires are liable to be disturbed the distance 
between supports must be shortened. 

At distributing centers, outlets or switches where space is 
limited and the five-inch separation cannot be maintained, each 
wire must be separately encased in a continuous length of ap- 
proved flexible tubing. 

In concealed knob and tube work the wires are supported 
on split knobs on the sides of joists and floor studdings and 
by porcelain tubes where passing through timbers. All wires 
must be separated one inch from the surface wired over so 
that the ordinary porcelain cleats must never be used for this 
work. 

Concealed knob and tube work was formerly used for all 
concealed work in frame buildings but many cities are now 
prohibiting its use for the following reasons : 

There is a great liability of disturbing the wires after they 
have been installed. 

No matter how careful the wireman may be in placing 
the wires other mechanics on the building are apt to place 
wood beams or other obstructions in contact with the wires 
after the wireman has left the work as completed. 

The porcelain bushings are very liable to be jarred out of 



192 



MODERN ELECTRICAL CONSTRUCTION. 



the joists through hammering in the laying of the floor or in 
the other work necessary to the completion of the building. 

Pipes or other metal work may be placed in contact with 
the wires either in completing the building or in changes re- 
quired after the building is completed. 

If a fire should for any reason start on the wires the rub- 




ber covering is very inflammable and might conduct the fire to 
the combustible woodwork surrounding the wires. 

Figure 71 shows the manner in which bushings are placed 
through the joists. The method shown in the upper part of 
the figure is preferable. In attics the wires must not be run 



LOW-POTENTIAL SYSTEMS. 1 93 

on the upper edges of joists as in this position they are con- 
sidered as exposed to mechanical injury (see Rule No. 26 f). 

s. When in a concealed knob and tube system, it is im- 
practicable to place the whole of a circuit on non-combustible 
supports of glass or porcelain, that portion of the circuit which 
cannot be so supported must be installed with approved metal 
conduit, or approved armored cable, except that if the differ- 
ence of potential between the wires is not over 300 volts, and 
if the wires are not exposed to moisture, they may be fished 
if separately encased in approved flexible tubing, extending in 
continuous lengths from porcelain support to porcelain sup- 
port, from porcelain support to outlet, or from outlet to outlet. 

An illustration of wiring on the "loop" system is shown in 
Figure 114. This system makes it unnecessary to have any 
concealed joints or splices. The amount of wire required is 
somewhat in excess of that required for tap systems, but this 
is often balanced by a saving in labor. Sometimes, however, 
the labor is also in excess of that required for tap systems. 
The main advantage of the system is that all joints and splices 
are always accessible. The figure also shows mixed "knob 
and tube" work and "conduit" work. Along the walls behind 
the furring strips there is seldom sufficient space to admit of 
knob and tube work and conduit must be used. 

Figure 115 is drawn to illustrate "fish work." Fish work is 
used in finished buildings, mostly, and is often very tedious 
and expensive. Hours are sometimes spent before wires can 
be brought through and often the effort is an entire failure. 
In combination work, as shown in Figure 103, there is usually 
little trouble, as there is the whole span between joists to run 
wires in. An effort to fish at right angles to the joists (when 
there are strips under joists) is more difficult, but often suc- 
cessful if the distance is not too great. 

When there are two men the usual method of fishing is : 
One man takes a wire sufficiently long to reach from one open- 
ing to the other, and, after bending a small hook on one end 



194 



MODERN ELECTRICAL CONSTRUCTION. 



in such a way that it will not catch easily on obstructions, 
pushes this end into one opening and, by twisting and working 
backward and forward, gradually forces it toward the other 
opening. At this opening his helper is stationed with a short 
wire, also provided with a hook, with which he must seek to 
catch the other wire when it comes near his opening. When 
the two wires come in contact, the larger one is drawn out and 
the conducting wires (encased in approved flexible tubing) 
are fastened to it and drawn through. The tubing should 
always be put on the wires before drawing in. If it is put on 




Figure 115. 



later there is much temptation to leave it as indicated at the 
right of the figure at a. This trick is quite common, but is 
very easily detected by inspectors ; the wire at either end can 
easily be pushed in without pushing out at the other, as it 
would if the tubing were continuous. If the tubing has been 
taped to the wires this will be impossible, but either one of the 
tubings can still be moved without moving the other, which 
would be impossible in a job properly done. The tubing must 



LOW-POTENTIAL SYSTEMS. 195 

consist of one piece, and there must be only one wire in each 
tubing. 

If one man is alone on a fish job, a handful of small wire 
is pushed into one opening in a manner which will allow it 
to spread out considerably. When the fish wire from the 
other opening comes in contact with it, it will indicate it by 
moving this wire, which can be seen by that left hanging out. 
A small fish wire is then used to draw out the long one. If 
the two openings are in different rooms and not visible, one 
from the other, a bell and battery can be used, as shown in 
the drawing, if there are no wire lath. 

When wires are to be entirely concealed it is nearly always 
necessary to find a way through headers, timbers, etc. ; this 
can hardly be done without cutting holes in plaster. A method 
doing as little damage as any is shown at the top in Figure 115. 
A hole is bored through the 2X4, which will allow the wire, 
when job is finished, to continue downward as shown by dotted 
lines, 1 and 2. Such turns are seldom ever used with electric 
light wires on account of their size ; they are more practicable 
with bell or telephone wires. 

Where it is desired to keep wires from showing in a parlor, 
for instance, they can be fished from an adjoining room, as 
indicated by dotted line 3, where the wires are run down 
partition in moulding in closet and then through to switch, 
which is in the same room with the lights. Before under- 
taking a job of fish work it is well to look the whole building 
over carefully. There are often false walls along chimneys, 
especially at both sides of mantels, in which wires can be 
easily run from basement to attic. 

Often it may be necessary to remove baseboards in order 
to find room for wires. When removing such boards never 
attempt to drive nails out, always break them off; if driven 
out they will usually split off parts of the board. 

Soft wood floors can easily be taken up when necessary. 



ig6 MODERN ELECTRICAL CONSTRUCTION. 

Use a broad thin chisel and cut away the tongue on each side 
of the board to be taken up ; the board can then be readily 
taken up. With double floors or with tightly laid hardwood 
floors, it is better to cut pockets in ceiling below. 

t. When using either conduit or armored cable in mixed 
concealed knob and tube work, the requirements for conduit 
work or armored cable work must be complied with as the 
case may be. 

u. Must at all outlets, except where conduit is used, be 
protected by approved flexible tubing, extending in continu- 
ous lengths from the last porcelain support to at least one 
inch beyond the outlet. In the case of combination fixtures the 
tubes must extend at least flush with outer end of gas cap. 

When the surface at any outlet is broken, it must be re- 
paired so as to leave no holes or open spaces at such outlet. 

It is suggested that approved outlet boxes or plates be installed 
at all outlets in concealed "knob and tube" work, the wires to 
be protected by approved flexible tubing, extending in continuous 
lengths, from the last porcelain support into the box. 

An installation of mixed concealed knob and tube work 
is shown in Figure 114. Where it is necessary to use conduit, 
as is often the case on brick walls, the conduit should extend 
from outlet to outlet (from the side bracket to the ceiling out- 
let in Figure 114). If there is no available outlet on the circuit 
a junction box should be placed at the ceiling line but in all 
cases this junction box should be accessible. The conduit 
should never end in the concealed space under the floor for, 
should the wire in the conduit burn out it would be impossible 
to replace it. The proper method for cases of this kind is 
shown in Figure 118. 

Figure 126 shows in detail the method of bringing wires 
out at a fixture outlet. The flexible tubing being carried flush 
with the lower end of the gas cap the wires will be protected 
when the fixture is put in place. It will be noted that the rule 
requires the flexible tubing to be continuous. The reason for 
this is quite evident for, were short pieces used, the wire might 



> 



LOW-POTENTIAL SYSTEMS. I97 

protrude at the point of connection and come in contact with 
the gas pipe. Figure 126 also shows the proper method of 
fastening a wire where it comes through a bushing at an out- 
let. In all cases the wires should be fastened under a knob 
after passing through the bushing so that they will not slip 
back and come in contact with the woodwork. 

There are probably more electrical fires started at fixture 
outlets than at any other point on the system and it is very 
essential that should a fire start at this point it be afforded no 
means for spreading. It will be noticed that when a hole is 
made in a ceiling in a frame building a strong draft is nearly 
always evident and for this reason care should always be taken 
to see that all openings into the concealed space back of the 
plaster are entirely closed. 

For Fixture Work. 

v. Must be not smaller than No. 18 B. & S. gage, and must 
have an approved rubber insulating covering (see No. 55). 

In wiring certain designs of show-case fixtures, ceiling 
bulls-eyes and similar appliances in which the wiring is ex- 
posed to temperatures in excess of 120 degrees Fahrenheit (49 
degrees Centigrade), from the heat of the lamps, approved 
slow-burning wire may be used. All such forms of fixtures 
must be submitted for examination, test and approval before 
being introduced for use. 

w. Supply conductors, and especially the splices to fixture 
wires, must be kept clear of the grounded part of gas pipes, 
and, where shell or outlet boxes are used, they must be made 
sufficiently large to allow the fulfillment of this requirement. 

x. Must, when fixtures are wired outside, be so secured 
as not to be cut or abraded by the pressure of the fastenings 
or motion of the fixture. 

y. Wires of different systems must never be contained or 
attached to the same fixture, and under no circumstances must 
there be a difference of potential of more than 300 volts be- 
tween wires contained in or attached to the same fixtures. 



I98 MODERN ELECTRICAL CONSTRUCTION. 

27. Armored Cables. 

(See also No. 26 s. For construction of Armored Cables see 

No. 57 .) 

a. Must be continuous from outlet to outlet or to junction 
boxes, and the armor of the cable must properly enter and 
be secured to all fittings, and the entire system must be me- 
chanically secured in position. 

In case of service connections and main runs, this involves 
running such armored cable continuously into a main cut-out 
cabinet or gutter surrounding the panel board, as the case 
may be. 

b. Must be equipped at every outlet with an approved out- 
let box or plate, as required in conduit work. 

Outlet plates must not be used where it is practicable to 
install outlet boxes. 

The outlet box or plate shall be so installed that it will 
be flush with the finished surface, and if this surface is broken 
it shall be repaired so that it will not show any gaps or open 
spaces around the edge of the outlet box or plate. 

In buildings already constructed where the conditions are 
such that neither outlet box nor plate can be installed, these 
appliances may be omitted by special permission of the Inspec- 
tion Department having jurisdiction, provided the armored 
cable is firmly and rigidly secured in place. 

c. Must have the metal armor of cables permanently and 
effectually grounded to water piping, gas piping or suitable 
ground plate, provided that when connections are made to gas 
piping, they must be on the street side of the meter. If the 
armored cable system consists of several separate sections, the 
sections must be bonded to each other, and the system 
grounded, or each section may be separately grounded, as re- 
quired above. 

The armor of cables and gas pipes must be securely fast- 
ened in outlet boxes, junction boxes and cabinets, so as to se- 
cure good electrical connection. 

If armor of cables and metal of couplings. outlet "boxes, junc- 
tion boxes, cabinets or fittings bavins: protective coating of non- 
conducting material, sucb as enamel are used, snob coating must 
be thoroughly removed from threads of both couplings and the 
armor of cables, and from surfaces of the boxes, cabinets and fit- 
tings where the armor of cables or ground clamp is secured in or- 



LOW-POTENTIAL SYSTEMS. 199 

der to obtain the requisite good connection. Grounded pipes should 
be cleaned of rust, scale, etc., at place of attachment of ground 
clamp. 

Connections to grounded pipes and to armor of cables must 
be exposed to view or readily accessible, and must be made by 
means of approved ground clamps, to which the ground wires 
must be soldered. 

Ground wires must be of copper, at least No. 10 B. & S. 
gage (where largest wire contained in cable is not greater than 
No. o B. & S. gage), and need not be greater than No. 4 B. & 
S. gage (where largest wire contained in cable is greater than 
No. B. & S. gage). They shall be protected from mechan- 
ical injury. 

d. When installed in so-called fireproof buildings in course 
of construction or afterwards if exposed to moisture, or where 
it is exposed to the weather, or in damp places, such "as brewer- 
ies, stables, etc., the cable must have a lead covering at least 
one thirty-second inch in thickness placed between the outer 
braid of the conductors and the steel armor. 

The lead covering is not to be required when the cable is 
run against brick walls or laid in ordinary plaster walls unless 
same are continuously damp. 

e. Where entering junction boxes, and at all other outlets, 
etc., must be provided with approved' terminal fittings which 
will protect the insulation of the conductors from abrasion, 

less such junction or outlet boxes are specially designed 
and approved for use with the cable. 

f. Junction boxes must always be installed in such a man- 
ner as to be accessible. 

g. For alternating current systems must have the two or 
more conductors of the circuit enclosed in one metal armor. 

h. All bends must be so made that the armor of the cable 
will not be injured. The radius of the curve of the inner edge 
of any bend not to be less than i 1 /^ inches. 

Armored Cable is made up of formed steel strips wound 
spirally over insulated conductors, the conductors themselves 
being given a slight twist to make them more flexible. Some 
manufacturers make the cable with a single strip of steel the 
outer edges of the strips being turned in so that adjacent 
edges interlock, as shown in Figure 116. To make the cable 



200 MODERN ELECTRICAL CONSTRUCTION. 

watertight a gasket is placed between the interlocking edges. 
This type of cable has the advantage that it is not apt to split 
open at bends, the interlocking feature preventing this, but it 
is not very flexible and has the disadvantage that where a 
sharp bend is required a careless workman is apt to "break" 
it, this being done by striking it a sharp blow over the edge of 



Figure 116. Figure 117. 

a bench and breaking the interlocking edges thus exposing the 
wire and straining the insulation. 

The double strip cable consists of two steel strips, one con- 
cave and the other convex. A section of this metal covering 
is shown in Figure 117. This cable is also made with a gasket 
to keep out water. It is more flexible than the single strip and 
is more generally used. 

In all types the metal strips are wound on such a diameter 
as to make it impossible to extract any great length of wire 
from the sheathing. 

Armored cable is very useful for the wiring or rewiring 
of old buildings and on account of its flexibility it may be in- 
stalled without any great damage to walls or ceilings. It 
possesses most of the desirable features of conduit work in so 
far as safety from fire is concerned. Its greatest objection lies 
in the fact that it is impossible to replace a burned out wire 
without replacing the whole cable and for this reason its use 
is mostly restricted to work in old buildings. If armored 
cable is "fished" in, and not fastened between outlets, it is 
always possible to replace any run in which trouble may 
develop. 

In the installation of armored cable the same general rules 
apply as for the installation of conduit. It must be provided 
with outlet boxes at all outlets, must be grounded, etc. 



LOW-POTENTIAL SYSTEMS. 201 

Where armored cable is run through holes bored through 
joists or is laid in notches cut in same it should be so placed 
that nails used in fastening down floors, especially hardwood 
floors, will not strike the metal armor, as under these condi- 
tions it is possible for a nail to be driven through the armor 
and make contact with the wires. While short circuits and 
grounds due to the cause just mentioned are not very common 
the expense of taking up floors may be considerable. 

Short bends should be avoided in the use of all armored 
cables. When the bend is short there is some strain which 
may cause the wire to come into contact with the metal strip 
of the armor. This will not produce bad effects at once but 
may do so after a long time. It is well also to test all coils 
of armored cable for continuity as well as for grounding or 
short circuits before installing. 

28. Interior Conduits. 

(See also No. 26 n to p. For construction of Conduit see No. 

58, and for construction of Outlet, Junction and Flush 

Switch Boxes see No. 59.) 

The object of a tube or conduit is to facilitate the insertion 
or extraction of the conductors and to protect them from me- 
chanical injury. Tubes or conduits are to be considered 
merely as raceways, and are not to be relied upon for in- 
sulation between wire and wire or between the wire and the 
ground. 

The installation of wires in conduit not only affords the 
wires protection from mechanical injury, but also reduces the 
liability of a short circuit or ground on the wires producing 
an arc, which would set fire to the surrounding material ; the 
conduit being generally of sufficient thickness to blow a fuse 
before the arc can burn through the metal of the pipe. For 
this reason the wires should be entirely encased in metal 



202 MODERN ELECTRICAL CONSTRUCTION. 

throughout, both in the conduit and at all outlets. Another 
advantage derived from the use of iron conduit is the facility 
with which wires can be extracted and replaced in case a 
fault develops on any of them. The saving which this may 
mean in cases where the installation of new wires would 
necessitate the destruction of costly decorations can readily be 
seen. 

It must be remembered that the arc or burn produced 

by a short circuit or ground is proportional to the size of the 
fuse protecting the circuit. If a large fuse, say 30 amperes, is 
used to protect a branch circuit and a ground or short occurs 
on this circuit, the wire may become fused to the pipe so that 
it cannot easily be pulled out. This is one reason why fuses 
should be as small as practicable. More than six amperes is 
seldom used on branch circuits, so that no larger fuse than 
this should ordinarily be used. The installation of wires in 
iron conduit also reduces the liability of lightning discharges 
entering a building as the pipe surrounding the wires offers 
great resistance to the passage of these sudden currents. 

Conduit is classed under two general heads, lined and un- 
lined. In both classes of conduit the same thickness of metal is 
required. Lined conduit is used but little at the present time. 

a. No conduit tube having an internal diameter of less 
than five-eighths of an inch shall be used. Measurements to 
be taken inside of metal conduits. 

This rule favors lined conduit insomuch that it requires 
the same pipe for lined and unlined, and allows a lined con- 
duit of less than five-eighths of an inch in diameter. 

Nominal one-half inch conduit has an internal diameter 
of five-eighths of an inch. 

b. Must be continuous from outlet to outlet or to junc- 
tion boxes, and the conduit must properly enter, and be secured 
to all fittings and the entire system must be mechanically se- 
cured in position. 



LOW-POTENTIAL SYSTEMS. 



203 



In case of service connections and main runs, this involves 
running each conduit continuously into a main cut-out cabinet 
or gutter surrounding the panel board, as the case may be. 

When conduit is used every run of pipe must end in acces- 
sible outlet boxes. This box may be a cut-out center, switch 
outlet, fixture outlet or a junction box. If a mixed form of 
wiring is used, where part of a circuit is run in conduit and 




* 



\ 



I 



—Junction box 



$*»•«*> 



r 



-Aot* -fcvrt 




**lf|\« 



t 



Figure 118. 



the balance with some other form of construction, such as 
concealed knob and tube work, for instance, the conduit must 
in all cases enter the box and be firmly attached to it, as 
shown in Figure 118. Cases are sometimes found where the 
conduit is brought just to the box, but does not enter it, the 
wires being extended through holes into the box. This method 
of wiring, is obviously wrong, as a wireman is apt to find if 
he ever has oocassion to replace wires in such a system. The 



204 



MODERN ELECTRICAL CONSTRUCTION. 



same holds true of cut-out centers. Here also every run of 
conduit must enter the box. The conduit should not simply 
be brought to the sides or the back of the cut-out center and 
the wires then carried to the cut-outs in flexible tubing, but 
every conduit should enter clear into the box so that when 






III 


- 1 


3 


. f 


^ 




'2 


• • 



ShcctStecl 

METER 




Figure 119. 



the work is completed there will be no exposed wiring. In 
the case of main runs the conduit should enter the boxes and 
never be broken between the outlets. Sometimes it is neces- 
sary to install meters on the mains and the conduit is ended 
and the wires carried to the meters and then either extended 
in conduit or carried into the cut-out center. This construc- 
tion should be avoided. If a meter is to be installed near a 
cut-out center, the main conduit should be carried into the box 
and the necessary meter loops then brought out. In this way 
the quantity of wire outside of conduits is reduced to a mini- 



LOW-POTENTIAL SYSTEMS. />5 

mum. If a meter is to be installed in some location along the 
mains other than at the cut-out center or service switch, a 
junction box should be provided and the meter loops brought 
out from that. This is shown in Figure 119, which also shows 
a cut-out box as used with conduit systems. 

c. Must be first installed as a complete conduit system, 
without the conductors. 

As fast as the conduit is installed, the ends of the pipes 
should be closed, using paper or corks. This lessens the liabil- 
ity of plaster or other substances entering the pipes and caus- 
ing trouble when the wires are to be pulled in. The con- 
ductors should not be pulled in until all the mechanical work 
on the building is, as far as possible, finished. When a 
conduit system is ready for the wires, the 'pulling in" may be 
done in various ways. For short runs, all that is necessary is 
to shove the wires in at one opening until they come out at 
the other. If a run is too long to be inserted in this way, 
what is known as a "fish wire" can be used. The ordinary 
fish wire is a flat band of steel about 5/32 inch wide and 1/32 
inch thick. This wire can be forced through any ordinary 
length of pipe. Ordinary round steel wire of about No. 12 
or 14 B. & S. gage can also be used, although this is not as 
good as the fish wire above described. 

The end of the wire is first bent back so as to form a very 
small hook or eye ; this will enable it to slide easily over ob- 
structions in the pipe and also make it possible should it stick 
somewhere to engage it with another fish wire provided with 
a suitable hook and entered from the other end of the pipe. 
This is very often necessary in runs having many bends. The 
fish wire, having been pushed through the pipe, is now fastened 
to the copper wire by means of a strong hook and the copper 
wire pulled into the pipe. 

In pulling in the large size cables, it is often found advan- 
tageous to pull on the fish wire and at the same time push on 



206 MODERN ELECTRICAL CONSTRUCTION. 

the end of the cable entering the pipes. It is also well to 
remember that it is easier to pull down than to pull up, as, 
when pulling down, the weight of the cable assists. The use 
of soapstone facilitates the drawing in of the wires. The wire 
may either be covered with the powdered soapstone or the 
soapstone may be blown into the pipes. An elbow partly 
filled with soapstone is often found convenient for blowing the 
soapstone into the pipe, always blowing from the highest point. 
Graphite or axle grease should never be used for this 
purpose, as the graphite is a conductor and the axle grease 
will rot the rubber insulating covering of the wire. 

d. Must be equipped at every outlet with an approved out- 
let box or plate. At exposed ends of conduit (but not at fix- 
ture outlets) where wires pass from the conduit system with- 
out splice, joint or tap, an approved fitting having separately 
bushed holes for each conductor is considered the equivalent 
of a box. 

Outlet plates must not be used where it is practicable to in- 
stall outlet boxes. 

The outlet box or plate must be so installed that it will be 
flush with the finished surface, and if this surface is broken 
it shall be repaired so that it will not show any gaps or open 
spaces around the edge of the outlet box or plate. 

In buildings already constructed where the conditions are 
such that neither outlet box nor plate can be installed, these 
appliances may be omitted by special permission of the Inspec- 
tion Department having jurisdiction, providing the conduit 
ends are bushed and secured. 

It is suggested that outlet boxes and fittings having con- 
ductive coatings be used in order to secure better electrical 
contact at all points throughout the conduit system. 

The object of an outlet box is to hold the conduits firmly 
in place, to connect the various runs of conduit so that they 
form a continuous electrical path to the ground, and to afford 
a fireproof enclosure for the joints, switches, etc. Outlet 
boxes are made in various designs to meet the requirements 
of the work on which they are to be used. 



LOW-POTENTIAL SYSTEMS. 20? 

Where it is impossible to use an outlet box, an outlet plate 
can be used. These plates are fitted with clamps so that 
they hold the ends of the conduits firmly in position and make 
the metal of the system continuous. They do not afford a 
fireproof enclosure for the joints and for that reason should 
never be used when it is practicable to use an outlet box. If 
the conditions are such that neither an outlet box nor plate can 
be used, special permission can be obtained from the Inspec- 
tion Department having jurisdiction to omit them. In this 
case the conduits should be bushed at the ends and the pipes 
should be bonded together. 

This rule requires that an outlet box or plate be used at 
every end of a run of conduit. For the ordinary switch, 
fixture, and like outlet suitable boxes are available. At ex- 
posed ends of conduit special fittings are on the market and 





Figure 120. 

should be used. These fittings are especially desirable for the 
following reasons: They separate the wires where they leave 
the conduit and thus tend to destroy any arc which might 
result at the weakest point of the conduit system; the point 
where the wires leave the pipe. They also provide an insu- 
lated bushing at that point at which the strain on the insula- 
tion of the wires is generally the greatest. They also serve- 
to separate the wires in a proper manner, when they leave the 
fitting. Fittings designed for this purpose are shown in Fig- 
ure 120. 



208 MODERN ELECTRICAL CONSTRUCTION. 

e. Metal conduits where they enter junction boxes, and at 
all other outlets, etc., must be provided with approved bush- 
ings or fastening plates fitted so as to protect wire from 
abrasion, except when such protection is obtained by the use 
of approved nipples, properly fitted in boxes or devices. 

When a piece of conduit is cut with a pipe cutter, a sharp 
<edge is left on the inside. This edge, if left on, would soon 
cut into the insulation of the wires. It should be removed by 
means of a pipe reamer. The bushing can now be screwed on 
as shown in Figure 118, a locknut having first been screwed 
onto the pipe. The locknut and bushing are then screwed up 
so that they are tight and form a good connection. 

f. Must have the metal of the conduit permamently and 
effectually grounded to water piping, gas piping or suitable 
ground plate, provided that when connections are made to gas 
piping, they must be on the street side of the meter. If the 
conduit system consists of several separate sections, the sec- 
tions must be bonded to each other, and the system grounded, 
or each section may be separately grounded, as required above. 
Where short sections of conduit (or pipe of equivalent 
strength) is used for the protection of exposed wiring on side 
walls, and such conduit or pipe and wiring is installed as re- 
quired by No. 26 e, the conduit or pipe need not be grounded. 

Conduits and gas pipes must be securely fastened in outlet 
boxes, junction boxes and cabinets, so as to secure good elec- 
trical connections. 

If conduit, couplings, outlet boxes, junction boxes, cabinets or 
fittings, having protective coating of non-conducting material such 
as enamel are used, such coating must be thoroughly removed from 
threads of both couplings and conduit, and such surfaces of boxes, 
cabinets and fittings where the conduit or ground clamp is se- 
cured in order to obtain the requisite good connection. Grounded 
pipes should be cleaned of rust, scale, etc., at place of attachment 
of ground clamp. 

Connections to grounded pipes and to conduit must be ex- 
posed to view or readily accessible, and must be made by means 
of approved ground clamps to which the ground wires must 
be soldered. 

Ground wires must be of copper, at least No. 10 B. & S. 
gage (where largest wire contained in conduit is not greater 



LOW-POTENTIAL SYSTEMS. 209 

than No. o B. & S. gage), and nee'd not be greater than No. 4 
B. & S. gage (where largest wire contained in conduit is 
greater than No. o B. & S. gage). They shall be protected 
from mechanical injury. 

That the metal in a conduit system should be permanently 
and effectually grounded is plainly evident when the hazards 
which are present with ungrounded or poorly grounded con- 
duit are recalled. Until recently very little attention has been 
given to the matter of properly grounding conduits, but with 
the increased use the necessity of so doing has become very 
apparent. If a bare wire on one side of a system comes in 
contact electrically with the iron pipe and if there is a ground 
on the other side of the system (and there always is with 3- 
wire systems) the conduit becomes a conductor. If the con- 
duit system is so installed that every piece is in good electrical 
connection and the entire system effectually grounded no 
harm will be done except the blowing of a fuse. 

Conduit is installed in all kinds of locations. It may be 
in contact with a gas pipe, lead pipe, or run in a damp floor, 
or it may be run exposed where a person could easily come in 
contact with it. The effects that might result from a conduit 
so run should the conduit become alive are readily seen. Sup- 
pose that in the first case the conduit crosses the gas pipe at 
right angles, the area of contact would be very small and the 
effect of the current in a livened conduit crossing this poor 
contact would result in burning a hole in the gas pipe and 
igniting the escaping gas. Again, suppose the conduit run in 
a damp floor should become alive ; the damp woodwork, being 
a conductor, would soon char and the charred part would 
then readily ignite. 

With a system which is grounded, an exposed piece of 
conduit will usually only be alive for a very short time 
during the blowing of the fuse. Even if it remains perma- 
nently alive, current will not flow from it to the surrounding 



210 MODERN ELECTRICAL CONSTRUCTION. 

material, but will take the easiest path to ground, which is 
along the conduit. On the ordinary branch circuits, the vari- 
our runs of conduit are bonded together through the outlet 
boxes and, in connecting the conduits to these boxes, care must 
be taken that they make good contact. In order to do this, the 
conduit should enter at right angles to the box and the enamel 
should be scraped away from the box so that the locknut and 
bushing make good electrical connection. The same thing 
should be done where the conduit enters the cut-out box. The 
metal of the cut-out box will bond together the various branch 
conduits and the main conduit. The main conduit should now 
be connected to some good ground, such as a water pipe or 
metal work of the building. Never carry the ground wire to 
a gas pipe unless on the street side of a meter. The various 
branch conduits should also be grounded wherever possible, 
at and on metal beams over which they cross and at every 
gas outlet. The reason of grounding the gas pipe thoroughly 
at the gas outlets is to be sure of a good ground. The gas 
pipe is necessarily in contact with the outlet box at this point 
and any poor contact which might cause arcing must be 
avoided. 

The rule specifies a No. 10 wire for grounding conduit 
where the wire in the conduit system is not larger than No. o. 
According to the table of carrying capacities a No. o wire will 
carry 127 amperes and while the No. 10 ground wire may be 
called upon to carry current sufficient to blow a fuse of this 
size, the current will last for but a short time and the ground 
wire will not have time to become dangerously hot. 

Special devices for attaching the ground wire to both the 
conduit and to grounded pipes are on the market and should 
always be used. Figure 121 shows two forms of ground 
clamps. 

When these are not obtainable a ground connection can be 



LOW-POTENTIAL SYSTEMS. 



211 



made by taking a number of good turns around the conduit and 
then soldering the wire to the conduit. A better way would 
be to use a few T couplings on the system and to screw brass 
plugs to these and solder the ground wire to the plugs. Such 





Figure 121. 



couplings should be installed near outlets where they will not 
interfere much with "fishing." 

If the ground wire has to be run for any great distance, 
it should be installed as though it were at all times alive, and 
should be kept away from inflammable material. 

The method advised under 15 for grounding wires should 
be used. Where a 3-wire system is used, the best ground oU- 



212 MODERN ELECTRICAL CONSTRUCTION. 

tainable is the neutral wire of the system. When a ground is 
made to the neutral wire, it should be made back of the fuses 
on the service switch ; never make the connection with the 
neutral inside of the service switch. 

g. Junction boxes must always be installed in such a man- 
ner as to be accessible. 

h. All elbows or bends must be so made that the conduit 
or lining of same will not be injured. The radius of the curve 
of the inner edge of any elbow not to be less than three and 
one-half inches. Must have not more than the equivalent of 
four quarter bends from outlet to outlet, the bends at the out- 
lets not being counted. 

If more than four quarter bends are necessary, a junction 
box should be installed and the wires first pulled from one 
of the outlets to the junction box and then from the junction 
box to the other outlet. 

Several methods are in use for bending conduit. With the 
lined conduit elbows and bends of various shapes can be 
obtained already bent, and it is much more satisfactory to use 
these, as considerable care must be exercised in making bends 
in order to keep the inside lining from coming loose from the 
pipe and causing trouble when "pulling in." To prevent this 
a suitable spiral spring is sometimes inserted into the con- 
duit before bending. Plumbers working with lead pipe often 
use coarse sand to fill the pipe before bending. This is more 
particularly useful with special conduits such as brass tubing, 
which is sometimes used in showcase or window work and 
classed with fixtures. 

With unlined conduits the bending is a simple matter, 
although here also care must be taken to see that the conduit 
does not bend flat. In a good bend the pipe retains its circular 
form throughout the bend, while, if the bend is poorly made, 
the pipe will assume an oval shape, flattening somewhat at 
the bend. The smaller size conduits can be bent in a common 



LOW-POTENTIAL SYSTEMS. 213 

vise. This is best accomplished by gripping the pipe in the 
vise and making a small bend, then moving the pipe for a slight 
distance and bending again, and continuing until the desired 
shape is obtained. This method, however, is not to be rec- 
ommended as, unless the wireman has had much experience on 
conduit work and is a very careful workman, the conduit will 
be more or less flattened at the bends. 

Another method which can be used on small pipes is shown 
at a in Figure 122, using a three or four foot length of gas 
pipe or conduit with an ordinary gas pipe T on the end. This 





Figure 122. 

is run over the conduit and gives sufficient leverage to make 
any bend. 

A simple device used for bending conduits is shown at b 
in Figure 122. This is constructed of metal, the wheel being 
grooved to fit the pipe. A similar device minus the wheel 
and lever may be made up of two blocks of wood firmly 
fastened to a work bench. The pipe can be bent around this 
by hand using a piece of pipe large enough to slip over the 
conduit to prevent it bending in the wrong place. In lieu of 
the pipe just mentioned a tee as shown at a Figure 122 may be 
used. 

For the larger conduits elbows can be obtained already 
bent, and the use of standard elbows for 90 degree bends in 



214 MODERN ELECTRICAL CONSTRUCTION. 

conduit I inch or larger is usually advisable. However, it is 
often necessary to make bends and offsets in large conduits. 
In order to bend large conduits some method of holding the 
conduit in place is necessary. This can often be done in new 
buildings by placing a heavy timber between the iron beams or 
columns and placing hard wood blocks on timber to hold the 
conduit in place. 

Connections between the various lengths of conduit are 
made with the ordinary gas-pipe couplings. When the conduit 
comes from the factory each length of pipe is provided with a 
coupling at one end. (This practice is now being discon- 
tinued, the couplings being left off.) This coupling should be 
removed and the end of the conduit reamed out. The reaming 




Figure 123. 

should always be done so that there is considerable metal left 
at the end of the pipe, and it should never be carried so far as 
to leave only a sharp edge. If a thread is to be cut, it is good 
practice to take a couple of turns with the reamer after this 
has been done. The coupling can then be screwed on. When 
making the connection, the pipes should be screwed into the 
coupling so that the ends just "butt." Do not attempt to screw 
them too tight, or, in all probability, the thread on the end 
of the pipe will be turned in and close the opening. Figure 
123, a, shows how a connection should be made. If lined con- 
duit is not properly reamed and is screwed too tight the 
opening is often entirely closed or forced downward, as shown 
at b. 

It is often necessary, especially in making changes in old 



LOW-POTENTIAL SYSTEMS. 215 

installations, to fit pieces between two pipes, neither one of 
which can be turned so as to draw them together. In such 
cases a long thread is cut on one piece of the pipe and the 
coupling run back on it; when the pipes are butted together 
the coupling is run over the two pipes, thus connecting them. 
A locknut may be run upon either pipe and used to keep the 
coupling in place. 

In running conduits avoid as much as possible passing 
through bath-rooms and other places where plumbers are likely 
to run their piping. 

When practicable, conduits should be run so they will 
drain; for instance, where crossing a room from one side 
bracket to another, it is better to run along ceiling than along 
the floor. Conduits will sometimes become quite moist inside 
from condensation. Where there is any likelihood of this the 
ends may be sealed. 

Figure 124 shows the wiring plan of a modern office build- 
ing. It will be seen from a close examination of the plan 
that there are several novel features in the layout of the 
circuits. The particular building to which this plan refers is 
designed for use as separate small offices or shops or the 
whole floor may be arranged for one tenant. 

In buildings of this class the final location of the outlets 
on the various floors is a subject of much uncertainty until 
the particular floor is rented and this may not be until after 
the rough work on the building is entirely completed. The 
usual method of placing conduit pipes together with switch 
and bracket outlets in partition walls necessitates either the 
altering of considerable conduit work to conform to the rent- 
ing plans, or that only a small proportion of the conduit can 
be put in place when the first portion of the work is done. 

With the layout shown by the floor plan no outlets or 
conduits are placed in any partitions. All circuits are carried 
to the outside walls of the building which, of course, are 
never altered. The conduits from the cutout center on each 
floor are large enough to carry additional circuits for future 
use and terminates in a 3-gang box. From this box conduits 



2l6 



MODERN ELECTRICAL CONSTRUCTION. 






& 



Pfc 




g ' ' ■ » 



Figure 124. 



LOW-POTENTIAL SYSTEMS. 21J 

extend on the ceiling in the direction of the first outlet. The 
conduit shown by the dotted lines is not run until the renting 
plans are available and the exact locations of ceiling outlets 
is secured. The 3-gang box referred to is arranged to be 
used for two switches and one receptacle or one switch and 
two receptacles, a special covering being provided so that 
these changes can be made at any time. 

It will be noted that only two ceiling outlets are installed 
on each conduit run, the usual method of cross connecting 
a number of outlets in a conduit net is avoided. This arrange- 
ment permits the outlets to be moved after installation with 
a minimum of labor and damage to the tile ceiling. 

Each of the conduit runs feeding towards the ceiling out- 
lets contains a separate 2-wire circuit. This arrangement 
permits partitions to be run between these outlets and the 
space divided up between columns in almost any manner 
without affecting the metering arrangement. 

With this wiring plan an unusually large percentage of 
conduit can be put in place when the work is first done and 
the final partition layout will not necessitate the changing of 
this pipe. 

29. Metal Mouldings. 

(See also No. 26 k to m. For construction of Mouldings see 

No. 60.) 

a. Must be continuous from outlet to outlet, to junction 
boxes, or approved fittings designed especially for use with 
metal mouldings, and must at all outlets be provided with ap- 
proved terminal fittings which will protect the insulation of 
conductors from abrasion, unless such protection is afforded 
by the construction of the boxes or fittings. 

b. Such moulding where passing through a floor must be 
carried through an iron pipe extending from the ceiling below 
to a point five feet above the floor, which will serve as an ad- 
ditional mechanical protection and exclude the presence of 
moisture often prevalent in such locations. 

In residences, office buildings and similar locations where 
appearance is an essential feature, and where the mechanical 
strength of the moulding itself is adequate, this ruling may be 



2l8 MODERN ELECTRICAL CONSTRUCTION. 

modified to require the protecting piping from the ceiling below 
to a point at least three inches above the flooring. 

c. Backing must be secured in position by screws or bolts, 
the heads of which must be flush with the metal. 

d. Must have the metal of moulding permanently and ef- 
fectually grounded to water piping, gas piping, or suitable 
ground plate, provided that when connections are made to gas 
piping, they must be on the street side of the meter. If the 
metal moulding system consists of several separate sections, 
the sections must be bonded to each other and the system 
grounded, or each section may be separately grounded, as re- 
quired above. 

Metal mouldings and gas pipes must be securely fastened 
to outlet boxes, junction boxes and cabinets, so as .to secure 
a good electrical connection. Moulding must be so installed 
that adjacent lengths of moulding will be mechanically and 
electrically secured at all points. 

If metal moulding, couplings, outlet boxes, junction boxes, cabinets 
or fittings have protective coating of non-conducting material such 
as enamel are used, such coating must be thoroughly removed from 
threads of couplings and metal mouldings, and from the surfaces 
of boxes, cabinets and fittings, where the metal moulding or 
ground clamp is secured in order to obtain the requisite good 
connection. Grounded pipes should be cleaned of rust, scale, etc., 
at the place of attachment of the ground clamp. 

Connection to grounded pipes and to metal mouldings must 
be exposed to view, or readily accessible, and must be made 
by means of approved ground clamps, to which the wires must 
be soldered. 

Ground wires must be of copper, at least No. 10 B. & S. 
gage. They shall be protected from mechanical injury. 

e. Must be installed so that for alternating systems the two 
or more wires of a circuit will be in the same metal moulding. 

It is suggested that this be done for direct systems also, so that 
they may be changed to the alternating system at any time, in- 
duction troubles preventing such change if the wires are in sepa- 
rate mouldings. 

Metal moulding is a comparatively recent development in 
wiring methods. It does away with a number of the ob- 
jectionable features that exist in the case of wood moulding, 
very closely resembling conduit in point of safety from fire. 
At the same time it retains most of the useful features of wood 



LOW-POTENTIAL SYSTEMS. 2IQ 

moulding. Its use is bound to become more extensive as 
many cities are now prohibiting the use of wood moulding en- 
tirely. 

It consists of a backing and a capping, both of metal, the 
backing being first fastened in place and the wires then laid in 
and covered by the capping. Figure 183 shows one form of 
metal moulding with some of the fittings. 

The rules governing its installation are very similar to 
those governing the installation of conduit and the explana- 
tions made under the head of conduit will apply equally 
well here. 

The thickness of metal not being as heavy as required for 
conduit it is more liable to mechanical injury and must 
therefore be protected on side walls. For the same reason 
its use is limited to circuits of not more than 660 watts 
(see Rule 26/), and not larger than 6 ampere fuses should 
ever be used for the circuit protection. 

30. Fixtures. 

(See also Nos. 24 e, 26 v to y and 55. For construction of Fix- 
tures see No. 77-) 
a. When supported at outlets in metal conduit, armored 
cable, or metal moulding systems, or from gas piping or any 
grounded metal work, or when installed on metal walls or 
ceilings, or on plaster walls or ceilings containing metal lath, 
or on walls or ceilings, in fireproof buildings, must be in- 
sulated from such supports by approved insulating joints 
placed as close as possible to the ceilings or walls. The 
insulating joint may be omitted in conduit, armored cable or 
metal moulding systems with straight electric fixtures in 
which the insulation of conductors is the equivalent of insula- 
tion in other parts of the system, and provided that approved 
sockets, receptacles or wireless clusters are used of a type 
having porcelain or equivalent insulation between live metal 
parts and outer metal shells, if any. 

Gas pipes must be protected above the insulating joint by 
approved insulating tubing, and where outlet tubes are used 



220 MODERN ELECTRICAL CONSTRUCTION. 

they must be of sufficient length to extend below the insulating 
joint, and must be so secured that they will not be pushed back 
when the canopy is put in place. 

Where insulating joints are required fixture canopies of 
metal in fireproof buildings must be thoroughly and perma- 
nently insulated from the walls or ceilings, and in other than 
fireproof buildings they must be thoroughly and permanently 
insulated from metal walls or ceilings or from plaster walls 
or ceilings on metal lathing. 

Fixtures having so-called flat canopies, tops or backs, will 
not be approved for installation, except where outlet boxes are 
used. 

The rule states very clearly what fixtures must be pro- 
vided with insulating joints. The primary reasons for re- 
quiring an additional insulation in the case of fixtures are : 
The wire used is of small size and the insulation quite thin. 
In the wiring of some forms of fixtures this rather poorly 
insulated wire is drawn in around all sorts of bends and 
angles and is generally subject to great abuse. The ordinary 
brass shell socket has the inner threaded portion separated 
from the outside shell only by a thin piece of prepared paper. 

It is therefore necessary to reduce the electrical strain 
on this insulation as much as possible and this is especially 
true of the insulation to ground. 

Another reason for the additional insulation is to pre- 
vent a ground on one fixture from causing trouble on other 
fixtures. If, for instance, one fixture in a building were in 
contact with the positive wire of the system and another in 
contact with a negative wire, and the two fixtures connected 
direct to the gas piping, the two contacts or "grounds" would 
form a short circuit, the current flowing from one pole along 
the gas piping to the other. This becomes impossible when 
the fixtures are insulated from the piping, or conducting 
parts of ceilings. 

Where a fixture is wired with a standard wire having at 



LOW-POTENTIAL SYSTEMS. 221 

least 3/64th inch rubber insulation and where the sockets 
are of porcelain or have a porcelain lining between the cur- 
rent carrying parts and the outer shell the objectionable 
features stated above no longer exist and the insulating joint 
is not required. 

Insulating joints are made in a variety of forms. The 
one shown at a Figure 125 is designed for use on a com- 
bination gas and electric fixture and is constructed so as to 
allow the gas to pass through. The insulating joint shown 
consists of malleable iron castings insulated with sheet mica 






Figure 125. 

and pressed together to form a joint strong enough to with- 
stand the strains put on it when the fixture is screwed into 
place. A hard rubber shell extends from one metal part to 
the other and prevents leakage over the joint from condensa- 
tion on its surface. 

In installing fixtures white or red lead should never be 
used on the threads to make them gas tight as these are 
liable to run down on the inside of the insulating joint and 
bridge the mica insulation separating the two parts of the 
joint. An insulating cement should be used for this purpose. 

The insulating joint shown at b, Figure 125 can be used 
with straight electric fixtures to attach the fixture to a stud 
in an outlet box or to a gas pipe. 



222 



MODERN ELECTRICAL CONSTRUCTION. 



Insulating joints should be placed as close as possible to 
the ceiling, so that there will be a minimum of exposed pipe 
above the joint. If the gas pipe has been left long so that 
the insulating joint comes some distance below the ceiling, 
it is necessary to protect the pipe above the joint either by 
using a porcelain tube which will fit over the pipe or by tap- 



} »»»^^< w/ m^ 




mszssmzssEzmzpsm 



.ube , t v 
xanop u uisilAwr 




Figure 126. 



ing the pipe thoroughly. Flexible tubing is also used. See 
Figure 126. 

In connecting the fixture, care should, be taken that the 
extra wire usually left for making the joint is twisted around 
the pipe below the insulating joint. If the wires at the out- 
let have been properly run, as shown in Figure 126, the flex- 
ible tubing, will extend to the bottom of the insulating joint. 

When a straight electric fixture is to be installed on some 
grounded part of the building, a crowfoot, shown at c, Fig- 
ure 125, can be fastened to the metal work and the fixture 
then connected with the insulating joint. 

If the fixture is to be mounted on plaster, a hardwood 
Mock can be screwed to the wall or ceiling and a crowfoot 
screwed to this. The screws holding the crowfoot must not 
extend through the block. Such a case is illustrated at the 
right in Figure 126. 



LOW-POTENTIAL SYSTEMS. 



223 



Before the plastering is put on, a board should be fastened 
between the joists, so that the wooden block may later be 
screwed to it. This is not absolutely necessary, as screws in 
lath will usually hold light fixtures. Heavy fixtures in old 
buildings can best be hung as shown at b, in Figure 127. This 
method is also used for ceiling fan motors. These motors 
must never be rigidly fastened, but should always be left 
free to swing and find their own centers. 

In connection with open or moulding work, the canopies 
should always be cut out, so that the loom or moulding may 




Figure 127. 



enter them. On no account should wires be allowed to 
rest on sharp edge of canopy. See a, Figure 127. 

Figure 127 illustrates at c how fixtures are fastened to 
tile ceilings, toggle bolts and a metal strip to which a piece 
of pipe is fastened being used. 

The "construction rules" covering insulating joints re- 
quire that the joint be capable of withstanding a voltage test 
of 4,000 volts. It is, of course, just as important that the 
canopies of fixtures be insulated from the walls or ceilings 
by an insulator capable of withstanding a like voltage test. 
Figure 128 shows a very acceptable type of canopy insulator, 
known as the "Bechtold" insulator. It is provided with a 



224 



MODERN ELECTRICAL CONSTRUCTION, 



slot into which the edge of the canopy fits. Small holes are 
punched at regular intervals through the inside wall and, 
by means of a special tool, the brass canopy is pressed -into 
these holes and the canopy insulator thus firmly held in placer 
Strips of fiber riveted or otherwise rigidly fastened to the 
canopy are frequently used. These strips must be not less 
than 1/16 inch in thickness and of sufficient width to allow 
a space of not less than 3/i6th inch between the metal canopy 
and the wall or ceiling. The fiber used for this purpose must 




be capable of withstanding the 4000 volt test previously de- 
scribed. Rivets or screws used to fasten the strips to the 
canopy should not be long enough to make contact with 
outlet boxes should these boxes be accidentally extended below 
the surface of the plaster. 

When a wooden block is used to fasten the fixture to the 
wall the block may be made large enough so that the canopy 
will rest against it and no further insulation is necessary. 
The practice of fastening the canopy a short distance away 
from the wall or ceiling does not comply with the rule. 



LOW-POTENTIAL SYSTEMS. 225 

With fixtures having flat backs no provision is made for 
the fixture and line wire necessary to make a joint and for 
this reason canopies of this type must only be used with out- 
let boxes where the wires can be pushed back into the box 
when the fixture is fastened in place. 

b. Must, when installed out doors, be of water-tight con- 
struction. 

c. Must not, when wired on the outside, be used in show 
windows or in the immediate vicinity of especially inflam- 
mable stuff. 

d. Must be free from short circuits between conductors 
and from contacts between conductors and metal parts of 
fixtures, and must be tested for such conditions before being 
connected to supply conductors. 

Three tests should be made on each fixture before it is con- 
nected. If tests are not made until fixtures have been con- 
nected, it is often necessary to disconnect them again to 
determine whether a fault is in the fixture or in the wir- 
ing. Where there are several fixtures on one circuit and a 
short circuit should be discovered, it would also likely be nec- 
essary to disconnect several of them before the right one 
would be found. 

A test for short circuit may be made, first, by connecting 
the two wires of a magneto to the two main wires at top 
of fixtures. If all sockets are properly connected and the 
wiring is clear, no ring will be obtained. If a ring is ob- 
tained, it indicates a short circuit. 

Without changing connections each socket may now be 
tested for connections. While one man is operating the mag- 
neto, another may insert a screw-driver, jack-knife, or piece 
of wire into each socket in turn, thus connecting the two 
terminals and causing a ring of the magneto. Failure to ob- 
tain a ring would indicate an open circuit, which must, of 
course, be remedied. 

The third test is made for "grounds." To make it, the 



226 MODERN ELECTRICAL CONSTRUCTION. 

two fixture wires are connected to one wire of the magneto 
and the other wire is connected to the metal of the fixture. 

It is best to connect this wire to the iron piping, and not 
to the lacquered brass; the lacquer is often a very good in- 
sulator. If a ring is now obtained, it indicates that the 
insulation on a wire has been damaged, and that the bare 
wire is in contact with the fixture. This test can be made 
more thorough by working the accessible fixture wires back 
and forth during the test; sometimes a damaged portion of 
wire is not in contact with the metal of fixture while lying 
upon the floor, but may be brought in contact with it when 
hanging. 

Fixtures that have been connected to the circuit and pro- 
vided with insulating joints can be individually tested for 
"grounds," by connecting one wire of a magneto to the body 
of the fixture and the other, first to one, and then the other, 
of the circuit wires in the sockets. This test will detect a 
"ground" in a fixture without disconnecting it from the cir- 
cuit. 

A battery and bell or, better still, an incandescent light 
in series on a lighting circuit may be used for the testing in 
place of the magneto. A telephone receiver and a small dry 
battery such as is used in pocket flash lamps forms a com- 
pact and very useful testing device. This may be carried 
without inconvenience in the pocket and is available for test- 
ing at any time. 

In connecting sockets to fixtures, it is advisable to con- 
nect them so that all protruding parts, as keys or receptacles 
for lamps, be of the same polarity, that is, all connected to 
the same main wire. This also applies to reflectors, border 
lights for theaters, encased in metal, etc. This will not lessen 
the liability of such parts to "ground," but lessens the chances 
of short circuits very much. Many "shorts" are brought 



LOW-POTENTIAL SYSTEMS. C j ] 

about by the projecting brass lamp butts on fixtures being 
of opposite polarity. If they are of the same polarity, they 
will cause no trouble. 

Special fixtures for show windows, etc, are often made up 
as shown in Figure 129. The construction shown at the 
left is more compart and neat, but requires more care in 
installing than the other, because of the edges of pipe in 




Figure 129. 

contact with the wires. If very long fixtures of this kind are 
installed/ it is advisable to insert insulating joints as often 
as practicable, even if necessary to run wires around them. 

31. Sockets. 

(For construction rules, see No. 72.) 

a. In rooms where inflammable gases may exist the in- 
candescent lamp and socket must be enclosed in a vapor-tight 
globe, and supported on a pipe-hanger, wired with approved 
rubber-covered wire soldered directly to the circuit. 

Key sockets contain a switch (see No. 17 b). 

In Figure 130, shows "vapor-tight" globes and Figure 
131,, a the method of suspending on a pipe hanger, the construe- 



228 



MODERN ELECTRICAL CONSTRUCTION. 



tion of which complies with the requirements of this rule. 
If moisture is present it is well to seal the upper end of the 
pipe with compound. 

Key sockets must not be used in rooms where inflam- 
mable gases exist. If enclosed as required above they would 
be useless. 

The reason for requiring vapor proof sockets to be sup- 
ported on pipe hangers is that they will be rigid and cannot 





Figure 130. 



be moved about sufficiently to come in contact with any ob- 
ject which might cause them to be broken. They should 
therefore be hung as high as circumstances will permit so 
that they will not be broken by being struck by anything "car- 
ried through the room. 

b. In damp or wet places "waterproof" sockets must be 
used. Unless made up on fixtures they must be hung by sep- 
arate stranded rubber-covered wires not smaller than No. 14 
B. & S. gage, which should preferably be twisted together 
when the pendant is over three feet long. 

These wires must be soldered direct to the circuit wires 
but supported independently of them. 

c. Key sockets will not be approved if installed over spe- 
cially inflammable stuff, or where exposed to flyings of com- 
bustible material. 



LOW-POTENTIAL SYSTEMS. 



229 



Waterproof sockets are constructed of porcelain, mica or 
moulded rubber as shown in Figure 132, and are not provided 
with keys, therefore the circuits to which they are connected 
must be controlled by switches. As a general rule these sock- 
ets are furnished with a short piece of stranded, rubber- 
covered wire extending through sealed holes in the top of 
the socket and the supporting wires are soldered to them. The 




Figure 131. 

method of suspending waterproof sockets varies with the con- 
ditions. Ordinarily, stranded rubber-covered wires of the 
proper length are suspended from single cleats as shown at 
b, in Figure 131, or, if the split knobs are large enough, the 
stranded wire may be supported from them. If the lamp is 
to be suspended only a short distance from the ceiling, where 
it will not be liable to be disturbed, it may be hung from two 
ordinary inch porcelain knobs, as shown in Figure 107. If 
cleats are used in a damp place for supporting the drop a half 



230 MODERN ELECTRICAL CONSTRUCTION. 

cleat must be provided back of the supporting cleat to give 
a one-inch separation, as required for wires in wet places. 

Moulded rubber sockets should not be used where oils 
or greases are present as these have a deleterious effect on 
the composition of which the socket is made. In some loca- 





Figure 132. 

tions porcelain sockets in which sulphur is used will break 
from the expansion of the sulphur. 

32. Flexible Cord. 

(For Construction of Flexible Cord see No. 54.) 

a. Must have an approved insulation and covering. 

b. Must not, except in street railway property, be used 
where the difference of potential between the two wires is 
over 300 volts. 

c. Must not be used as a support for clusters. 

d. Must not be used except for pendants, wiring of fix- 
tures, portable lamps or motors, and portable heating ap- 
paratus. 

For all portable work, including those pendants which are 
liable to be moved about sufficiently to come in contact with 
surrounding objects, flexible wires and cables especially de- 
signed to withstand this severe service must be used. 

When necessary to prevent portable lamps from coming 



LOW-POTENTIAL SYSTEMS. 23 1 

in contact with inflammable materials, or to protect them 
from breakage, they must be surrounded with a substan- 
tial wire guard. 

Under the heading of flexible cord are all the various 
types of flexible wires such as, common pendant cord, port- 
able cord, stage cable, etc., and the construction rules, No. 
54, should be very carefully read. 

The practice of making pendant cords unnecessarily long 
and then looping them up with cord adjusters is strongly ad- 
vised against. It offers a temptation to carry about lamps 
which are intended to hang freely in air. These adjusters 
should never be used where their use can be avoided and 
where they are used should only be placed on lamps which 




Figure 133. 

will seldom need adjusting. The indiscriminate use of cord 
adjusters cannot be too strongly condemned as the constant 
rubbing of the adjuster soon destroys the insulation. 

At c, Figure 131, shows a brass socket threaded for }i~ 
inch pipe, and which is designed to be used with portable 
£ord. Care should be taken in making up these sockets to 
see that the knot under the head of the socket has a good 
bearing surface so that it will not pull through the larger 
bushing, these portables being very apt to be jerked about. 

A lamp guard to be of any value should be so constructed 
that the bulb of the lamp cannot come in contact with any- 
thing outside of the lamp guard; it should also protect the 
lamp from any sudden jar. The design of the guard should 
be such that it can be firmly attached to the socket so it will 



2$2 MODERN ELECTRICAL CONSTRUCTION. 

not work loose and come in contact with the live butt of the 
lamp or projecting threaded portion of the socket. See Fig- 
ure 133. 

e. Must not be 'used in show windows or show cases ex- 
cept when provided with an approved metal armor. 

The great number of fires which have been caused by* the 
use of flexible cord in show windows is sufficient argument 
against its use. 

f. Must be protected by insulating bushings where the 
cord enters the socket. 

g. Must be so suspended that the entire weight of the 
socket and lamp will be borne by some approved method un- 
der the bushing in the socket, and above the point where the 
cord comes through the ceiling block or rosette, in order that 
the strain may be taken from the joints and binding screws. 

This is usually accomplished by knots in the cord inside 
the socket and rosette. 

Special ceiling blocks or rosettes which facilitate the fas- 
tening of cords are on the market and should be used. In 
fastening the cord to the binding screws it is advisable to 
solder the ends of the wire. This, however, is not required 
by the rule (see No. 16 c) , and should not be attempted un- 
less great care is to be taken. If the ends of the cord are 
soldered stray strands of wire are not liable to come in con- 
tact with the brass shell of the socket and a much stronger 
and better contact is obtained at the binding screw. If a 
blow torch is used the small wires are very liable to be over- 
heated and become brittle. The rubber insulation is also 
liable to be destroyed and it will soon crack and fall oft. The 
soldering can best be done with a soldering iron or by dip- 
ping the ends in molten solder being careful to keep the in- 
sulating covering of the wires from becoming overheated. 

It is also well to tape the ends of cords, leaving only 



LOW-POTENTIAL SYSTEMS. 



233 



just enough bare metal to go under the binding screws; the 
tape will hold the end of the braid and will confine any ends 
of wires which do not happen to come under the binding 
screws. 

33. Arc Lamps on Constant-Potential Circuits. 

(For construction of Arc Lamps see No. 74.) 

a. Must have a cut-out (see No. 19 a) for each lamp or 
each series of lamps. 

The branch conductors should have a carrying capacity 
about 50 per cent in excess of the normal current required 
by the lamp. 

Figure 134 at the left gives a diagram of a constant poten- 
tial arc circuit as generally used at present for enclosed arc 




Figure 134. 



lamps. Each arc lamp of this kind requires a pressure of 
no volts. A steadying resistance, R, is always placed in series 
with constant potential lamps, its object being to keep down 
the current while the lamp feeds. During the short time that 
the two carbons are together, the resistance of the lamp is 
so low that an enormous amount of current would flow were 
it not for this resistance. With most lamps this resistance 
is now installed in the hood. Since the rule requires a car- 
rying capacity about 50 per cent in excess of the normal cur- 



234 MODERN ELECTRICAL CONSTRUCTION. 

rent for branch conductors, it would be well to provide this 
also for mains in such cases where groups of arc lamps are 
likely to be controlled by one switch and used together. 

Figure 134 at the right shows a diagram of wiring for flam- 
ing arc lamps. Two lamps are usually run in series on no 
volts together with a steadying resistance. 

b. Must only be furnished with such resistance or regula- 
tors as are enclosed in non-combustible material, such resist- 
ances being treated as sources of heat. Incandescent lamps 
must not be used for this purpose. 

c. Must be supplied with globes and protected by spark 
arresters and wire netting around the globe, as in the case of 
series arc lamps (see No. 21). 

Outside arc lamps must be suspended at least eight feet 
above sidewalks. Inside arc lamps must be placed out of 
reach or suitably protected. 

d. Lamps when arranged to be raised and lowered, either 
for- carboning or other purposes, shall be connected up with 
stranded conductors from the last point of support to the 
lamp, when such conductor is larger than No. 14 B. & S. 
gage. 

This is required as a solid wire is apt to break from the 
constant swinging of the wires from the wind and from the 
raising and lowering of the lamp. 

34. Mercury Vapor Lamps. 

Enclosed Mercury Vapor Lamps. 

a. Must have cut-out for each lamp or series of lamps 
except when contained in single frame and lighted by a single 
operation, in which case not more than five lamps should be 
dependent upon single cut-out. 

b. Must only be furnished with such resistances or reg- 
ulators as are enclosed in non-combustible cases, such re- 
sistances to be treated as sources of heat. In locations where 
these resistances or regulators are subject to flyings of lint 
or combustible material, all openings through cases must be 
protected by fine wire gauze. 



LOW-POTENTIAL SYSTEMS. 



235 



The Cooper-Hewitt mercury vapor lamp is shown 
diagramatically in Figure 135. It consists of a long glass 
tube at one extremity of which is a metal reservoir partially 
rilled with mercury. The lamp may be started by tilting the 
tube to a horizontal direction when the mercury flows out of 
the reservoir and forms a metallic stream connecting elec- 
trically the two terminals at each end of the lamp. As soon 
as the circuit is established the lamp is released and the mer- 
cury flows back into the reservoir but the current continues 
to flow through a path afforded by the mercury vapor. A 
greenish light is produced. 

So far as the installation rules are concerned, this lamp 
is similar to the arc lamp. A resistance is always provided 




s-MK 



Figure 135. 



to hold down the starting current when the lamp is short 
circuited by the stream of mercury and also to adjust the 
lamp to the proper current. Lamps are run either singly or 
two in series on no volts or four in series on 220 volts, and for 
photographic work they are mounted in a frame, but in ac- 
cordance with the rule, more than five lamps must never be 
dependent on one cut-out. 

High-Potential Vacuum Tube Systems. 

c. The tube must be so installed as to be free from me- 
chanical injury or liability to contact with inflammable 
material. 



236 MODERN ELECTRICAL CONSTRUCTION. 

d. High-potential coils and regulating apparatus must be 
installed in approved steel cabinet not less than one-tenth 
inch in thickness ; same to be well ventilated in such a man- 
ner as to prevent the escape of any flame or sparks, in case 
of burnout in the various coils. All apparatus in this box 
must be mounted on slate base and the enclosing case posi- 
tively grounded. Supplying conductors leading into this high- 
potential case to be installed in accordance with the standard 
requirements governing low-potential systems, where such 
wires do not carry a potential of over 300 volts. 

The Moore tube is the best known vacuum tube lighting 
system. This system of lighting has not come into any gen- 
eral use as it is still in a more or less experimental stage. 
It consists of a long gas tight tube carried around the space 
to be lighted. This tube is filled with a gas and the kind of 
gas used determines the character of the light. A high 
potential produced by specially designed transformers causes 
the current to flow through the gas in the tube. 

35. Economy Coils. 

a. Economy and compensator coils for arc lamps must 
be mounted on non-combustible, non-absorptive, insulating 
supports, such as glass or porcelain, allowing an air space of 
at least one inch between frame and support, and must in 
general be treated as sources of heat. 

Economy or compensator coils are used in connection with 
arc lamps on multiple alternating current circuits. They 
serve the same purpose that the resistance coil does on the 
direct current arc lamp, but unlike the resistance they op- 
erate without the development of any great amount of heat. 
Some heat is, however, produced and these coils must be 
mounted away from woodwork or other combustible mate- 
rial. 



LOW-POTENTIAL SYSTEMS. 237 

36. .Transformers. 

(See also Nos. n, 14, 15 and 45. For construction of 
Transformers see No. 81.) 

Oil transformers : — 

a. Must not be placed inside of any building except cen- 
tral stations and sub-stations, unless by special permission of 
the inspection department having jurisdiction. 

Air cooled transformers : — 

The following sections do not apply to apparatus or 
fittings, the operation of which depends either wholly 
or in part upon special transformers embodied in the 
devices, but all such apparatus or fittings must be sub- 
mitted for special examination and approved before 
being used. 

b. Must not be placed inside of any building excepting 
central stations and sub-stations, if the highest voltage of 
either primary or secondary exceeds 550 volts. 

c. Must be so mounted that the case shall be at a dis- 
tance of at least one foot from combustible material or sep- 
arated therefrom by non-combustible, non-absorptive, insulat- 
ing material, such as slate, marble or soapstone. This will 
require the use of a slab or panel somewhat larger than the 
transformer. 

Oil cooled transformers are objectionable when installed 
inside of a building because the transformer has within it all 
that is necessary to both start a fire and to spread it after 
once started. For this reason the rule forbids them inside 
of the ordinary building. There are special conditions how- 
ever, where oil cooled transformers must be used and in 
such cases the inspection department having jurisdiction must 
be consulted before installation. 

37. Decorative Lighting Systems. 

a. Special permission may be given in writing by the In- 
spection Department having jurisdiction for the temporary 
installation of approved Systems of Decorative Lighting, pro- 



238 MODERN ELECTRICAL CONSTRUCTION. 

vided the difference of potential between the wires of any cir- 
cuit shall not be over 150 volts and also provided that no 
group of lamps requiring more than 1,320 watts shall be de- 
pendent on one cut-out. 

The Elblight decorative lighting system is approved for 
temporary installations. This system consists of a pair of 
heavy copper wires made up with fine copper strands. The 
wires are insulated and covered with an unsaturated braid. 
Receptacles for use with these wires are of porcelain, the 
terminals being two pointed pins which are stuck into the 
wire through the insulation, the pins entering the fine strands 
and making contact. The receptacles are held to the wire 
by porcelain pieces which clamp around the two wires. Re- 
ceptacles may be attached to the wire at any point but in no 
case must more than 1320 watts be dependent on one cut-out. 

Other decorative lighting systems are limited mostly to 
Christmas tree lights. There are a great number of these 
on the market and some of them are dangerous and should 
not be used. The list of approved fittings issued by the 
Underwriters laboratories should be consulted to determine 
those safe to use. 

38. Theatre and Moving Picture Establishment Wiring. 

All wiring, apparatus, etc., not specially covered by special 
rules herein given, must conform to the standard rules and 
requirements of the National Electrical Code, and the term 
"theatre" shall mean a building, or that part of a building 
regularly or frequently used for dramatic, operatic, moving 
picture or other performances or shows or which has a stage 
for such performances used with scenery or other stage 
appliances. 

a. Services. 

Where supply may be obtained from two separate street 
mains, two separate and distinct services must be installed, 
one service to be of sufficient capacity to supply current for 
the entire equipment of theatre, while the other service must 



LOW-POTENTIAL SYSTEMS. 239 

be at least of sufficient capacity to supply current for all 
emergency lights. Where supply cannot be obtained from 
two separate sources, the feed for emergency lights must be 
taken from a point on the street side of main service fuses. 
By "emergency lights" are meant exit lights and all lights 
in lobbies, stairways, corridors, and other portions of theatre 
to which the public have access, which are normally kept 
lighted during the performance. 

Where source of supply is an isolated plant within same 
building, an auxiliary service of at least sufficient capacity 
to supply all emergency lights must be installed from some 
outside source, or a suitable storage battery within the prem- 
ises may be considered the equivalent of such service. 

The spirit of this rule requires that the 'emergency" light- 
ing system be kept entirely separate and distinct from the 
general lighting system. The emergency lighting system is 
designed to provide illumination sufficient for the audience to 
get from the auditorium to the outside of the building un- 
der any and all conditions liable to exist, even where the gen- 
eral illuminating system has been rendered useless. It is, 
therefore, of the utmost importance that the emergency sys- 
tem be made as reliable as is possible to the end that under 
no condition liable to exist will these lights be out of serv- 
ice. Figure 136 shows how this rule and also e-4 may be 
complied with. The emergency circuit should if possible be 
taken from mains that have no connection whatever with 
those supplying the auditorium and stage lights. The emer- 
gency mains must lead to the lobby and are not allowed 
to have any fuses except those at the street and those finally 
protecting the branch circuits. Under certain interpretation 
of this rule it is permissible to connect the two systems as 
shown by dotted lines. This is, however, bad practice, as the 
switch may be unintentionally left as shown in the cut and 
thus when the main fuse blows all of the lights will be out. 
In many cases this arrangement will be very costly, as often 
lobby and theater mains do not run close together. As, 



240 



MODERN ELECTRICAL CONSTRUCTION. 



there is to be only one fuse between street and cut-out box, 
the mains to lobby will have to be of the same size as the 
house mains. 



r^^—^ 



■ca 



■ca 



P o 



3 



o 



fcs 



CABINET 

InLobby. 



CweRGEKiCY 

Service. 




ERMETGEtMC^ 

Light 
Circuits 



M A)N F*OR HOW SE ANO STAGE. 




Main 
Service* 



Figure 136. 

It will be a good plan to arrange the house mains as 
shown in Figure 137. The double throw switch is provided 



LOW-POTENTIAL SYSTEMS. 



241 



merely to enable a quick re-illumination to take place in case 
one of the fuses were to blow. The switch is located at the 
electrician's station and it is but necessary for him to throw 
the switch to the other side to light up the house again. 

In order to be certain that the fuse in the street will not 
blow, the wires between street and switch may be made sev- 



SJ 



Figure 137. 



eral sizes heavier than required and fused accordingly. Un- 
der such circumstances it is extremely unlikely that any 
but the fuse at the electrician's station will blow. 

b. Stage. 

All permanent construction on stage side of proscenium 
wall, except as hereinafter provided, must be approved con- 
duit or armored cable. 

c. Switchboards. 

Must be made of non-combustible, non-absorptive insulat- 
ing material, and where accessible from stage level must be 
protected by a suitable guard rail to prevent accidental con- 
tact with live parts on the board. 



242 



MODERN ELECTRICAL CONSTRUCTION. 



The switchboard of necessity being close to the stage 
proper is generally in such a position that persons leaving 
the stage pass directly in front of it. As the costumes worn 
by actors are very often made up of tinsel or other conduct- 





Figure 138. 



ing material, and as various metal trappings are carried, it 
is essential that the guard rail be of such design as to pre- 
vent these materials from coming in contact with the live 
parts of the board. Where the guard rail is placed close to 



LOW-POTENTIAL SYSTEMS. 243 

the board it is often advisable to provide a screen between 
the guard rail and the floor. 

The best method, however, so far as safety is concerned 
is that of elevating the switchboard so that there can be no 
interference with it. 

d. Footlights. 

Must be wired in approved conduit or armored cable, each 
lamp receptacle being enclosed within, an approved outlet box, 
or the lamp receptacles may be mounted in an iron or steel 
box, metal to be 'of a thickness not less than No. 20 U. S. 
Sheet Metal gage treated to prevent oxidation, so constructed 
as to enclose all the wires. Wires to be soldered to lugs of 
receptacles. 

Must be so wired that no set of lamps requiring more than 
1,320 watts nor more than 24 receptacles shall be dependent 
upon one cut-out. 

Figure 138 shows a number of forms in which footlight 
troughs are made up. These troughs are constructed of No. 




•^nmq&gHRfifl 



Figure 139. 

20 U. S. sheet metal gage iron or steel, the receptacles be- 
ing attached to the upper section as shown in Figure 139. 
The completed footlight strip is shown in Figure 140. These 
strips are combined in various ways to make up the foot- 



244 MODERN ELECTRICAL CONSTRUCTION. 

light proper, their arrangement depending on the lighting 
effect desired. A common arrangement is shown in Figure 
141, where two separate strips are used, one elevated above 
the other in order that the light from the back row of lamps 
will not be obstructed by the lamps in the front row. When 




Figure 140. 



footlights are installed in this manner more light is obtained 
when the clear lamps are placed in the front row, as only 
a small part of the light emitted from the colored lamps will 
be absorbed by passing through the clear globes, while, with 
the reverse arrangement, where the colored lamps are placed 




Figure 141. 

in the front row, a considerable amount of light would be ab- 
sorbed by the light from the clear lamps passing through the 
colored glass. Owing to the fact that the footlights are gen- 
erally placed in troughs cut in the stage floor, thus bringing 
the lamps below the level of the stage floor, the placing of 
the white lamps in the lower row would not allow sufficient 



LOW-POTENTIAL SYSTEMS. 245 

light to illuminate the back part of the stage, and for this 
reason where footlights are placed as shown in the figure it 
is the usual practice to place the white lights in the upper 
row. 

Where all the lamps, both white and colored, are placed 
in one row, a reflector of the design shown in Figure 142 
will materially increase the useful light. 

Receptacles used in footlight construction must be of ap- 
proved design and where the receptacle is fastened to the 
metal work with porcelain or metal threaded rings the re- 
ceptacle must be so designed that it cannot be turned by the 
insertion or extraction of the lamp. This is generally ac- 
complished by means of notches or projections on the porce- 



^Q^QsO^Q-Q/ 



Figure 142. 

lain of the receptacle and the metal should always be stamped 
to fit these parts. 

Double braid, rubber covered wire must be used, and, 
with clip sockets, the wire must be soldered to the clip, in 
addition to being fastened by the binding screws. If the 
porcelain of the receptacle does not provide proper protec- 
tion all exposed contacts, including the clips themselves, 
should be taped or covered with a suitable compound. Com- 
pound should not be used on border lights, as the heat from 
the lamps will cause the compound to melt and run down on 
the lamps. This also applies to any device of this form 
where the lamp hangs down, or below, the trough. In cases 
of this kind the clips should be taped, or, better, properly de- 
signed receptacles used. 

The footlight circuits may be wired for a capacity of 1,320 



246 .MODERN ELECTRICAL CONSTRUCTION. 

watts, this allowing 24-16 c. p. lamps, 18-24 c. p. lamps, or 
12-32 c. p. lamps of the carbon filament type on one circuit. 

e. Borders and Proscenium Sidelights. 

1. Must be constructed of steel of a thickness not less 
than No. 20 U. S. Sheet Metal gage, treated to prevent 
oxidation, be suitably stayed and supported, and so designed 
that flanges of reflectors will protect lamps. 

2. Must be so wired that no set of lamps requiring more 
than 1, 320 watts nor more than 24 receptacles shall be de- 
pendent upon one cut-out. 

3. Must be wired in approved conduit or armored cable, 
each lamp receptacle to be enclosed within an approved out- 
let box, or the lamp receptacles may be mounted in an iron 
or steel box, metal to be of a thickness not less than No. 20 
U. S. Sheet Metal gage treated to prevent oxidation, so con- 
structed as to enclose all wires. Wires to be soldered to 
lugs of receptacles. 

4. Must be provided with suitable guards to prevent 
scenery or other combustible material coming in contact with 
lamps. 

5. Cables for borders must be of approved type and suit- 
ably supported ; conduit construction must be used from 
switchboard to point where cables must be flexible to permit 
of the raising and lowering of border. 

6. For the wiring of the border proper, wire with ap- 
proved slow-burning insulation must be used. 

7. m Borders must be suitably suspended, and if a wire 
rope is used same must be insulated by at least one strain 
insulator inserted at the border. 

The design and construction of border lights is similar to 
that just described for footlights with the exception of the 
arrangement of the strips and the kind of wire used. Bor- 
der lights are suspended above the stage and are designed to 
throw the light downward and slightly to the back of the 
stage. To produce the proper lighting effects the border must 
be capable of adjustment, both as to its height above the 
stage and its position. 



LOW-POTENTIAL SYSTEMS. 



247 



Figure 143 shows several forms of border lights. 
Figure 144 shows a simple form of border light in com- 
mon use. It will be noticed that the flange of the reflector is 



<2 



3 











Figure 143. 



carried around the lamps in such a manner as to protect them 
from accidental contact with the scenery. 

Figure 145 shows a completed border light with one 
method of suspension. The iron bands to which are fas- 
tened the supporting chains are carried entirely around the 
border frame and serve as a means of attaching it to its 
support and at the same time provide mechanical protection 




Figure 144. 



for the lamps. These bands are placed from four to six feet 
apart. 

The cables which carry current to the border lights are 
generally made up for each individual installation, the size 
and number of wires varying according to the number and 



248 



MODERN ELECTRICAL CONSTRUCTION. 



combination of lamps used and the distance of the border 
from the stage switchboard or center of distribution. 

See 54 f for specifications governing border cables. 

The cables should be long enough to allow the border to 
be lowered to within six or seven feet of the floor to permit 
of the necessary repairs and adjustments and the replacement 
of lamps. 

"Take-up" devices, which are attached to the cable to take 
up the slack when the border is raised, should be fastened 
to the cable by some suitable device which will give a large 




Figure 145. 



bearing surface so that the insulation of the cable will not 
be injured. The practice of simply tying a rope around the 
cable is very bad, as the rope is sure to cut into the insulation. 
As considerable heat is developed in a border light, due to 
the great number of lamps employed and to the position of 
the border itself, the rubber covering of the ordinary rubber 
covered wire would be very apt to become useless as an in- 
sulator, so that for this class of wiring slow-burning wire 
should be used. Specifications covering this wire are given 
under "Fittings. " 



LOW-POTENTIAL SYSTEMS. 249 

Wire rope must be used for the suspension of the border 
lights. The rope should be of such size as to properly sup- 
port the border with an ample safety factor. Generally three 
or four ropes are provided, each rope being fastened to a 
bridle which will distribute the strain uniformly along the 
length of the border frame. A strain insulator of the 
type shown in Figure 53 should be connected in- the cable at 
the point where it connects to the border. The supporting 
cables are generally run to counterweights, hemp ropes fas- 




Figure 146. 

tened to either the counterweights or the border itself serv- 
ing as a means to raise and lower the border. Where the 
border is small and of inconsiderable weight the wire rope is 
run directly to the point of fastening and the adjustments 
made with it direct. The supporting cables should be kept 
well oiled, dampness, especially that due to fire proofing of 
scenery is very likely to rust them. 

Those lights placed at the stage opening on the stage side 
of the wall which separates the stage from the auditorium 
(prosecenium wall) are known as the proscenium side lights. 
They are constructed in the same manner as the footlights 
previously described, with the exception of the reflectors, 
which are of various shapes. Figure 146 shows a common 
form of proscenium side light. 



250 MODERN ELECTRICAL CONSTRUCTION. 

The troughs are generally hinged so that they may be 
turned to illuminate any particular part of the stage, and 
special care should be exercised in placing them so that they 
cannot in any manner interfere with the operating of the 
curtain. It is sometimes advisable, especially in the case of 
vaudeville or burlesque houses, to provide a wire mesh screen 
for the protection of the lamps. 

/. Stage and Gallery Pockets. 

Must be of approved type, controlled from switchboard, 
each receptacle to be of not less than 35 ampere rating for 
arc lamps nor 15 amperes for incandescent lamps, and each 
receptacle to be wired to its full capacity. Arc pockets to be 
wired with wire not smaller than No. 6 B. & S. gage and in- 
candescent pockets with not less than No. 12 B. & S. gage. 

Plugs for arcs and incandescent pockets must not be inter- 
changeable. 

For the connection of portable apparatus on the stage or 
the gallery pockets are provided generally in the floor. These 
pockets contain receptacles into which the plugs connected to 
cables attached to the apparatus are inserted. The pockets 
should be made absolutely fireproof and the receptacles should 
be so installed that all live parts will be clear of the opening. 
It is now required to have stage plugs of different designs to 
be used in connection with arc and incandescent lights, so 
that it will be impossible to plug incandescent lights on arc 
light circuits. An arc light circuit requires a fuse of about 
forty amperes. Many times a single incandescent light is 
plugged into such a circuit. A short circuit occurring under 
these circumstances would be accompanied with disastrous 
results. Figure 147 shows a stage pocket with receptacles. 
The average stage pocket accommodates four receptacles. 



LOW-POTENTIAL SYSTEMS. 



251 



g. Scene Docks. 

Where lamps are installed in Scene Docks, they must be 
so located and installed that they will not be liable to me- 
chanical injury. 

As scene docks are often used for the storage of scenery 
and other stage paraphernalia and as lights are generally 
placed on the side walls, a substantial guard should be pro- 
vided. This guard should be capable of standing considerable 





Figure 147. 



hard usage and should be firmly attached. The ordinary lamp 
guard fastened to the socket or lamp itself is useless as a 
protection. 

h. Curtain Motors. 

Must be of ironclad type and installed so as to conform 
to the requirements of the National Electrical Code. (See 
No. 8.) 

Rheostats used with curtain motors, if installed on the 

stage wall or in any other location outside of the motor room, 



252 MODERN ELECTRICAL CONSTRUCTION. 

should be entirely enclosed and well protected, so that noth- 
ing of an inflammable nature can come in contact with them. 

j. Control for Stage Flues. 

In cases where dampers are released by an electric device, 
the electric circuit operating same must be normally closed. 

Magnet operating damper must be wound to take full volt- 
age of circuit by which it is supplied, using no resistance 
device, and must not heat more than normal for apparatus of 
similar construction. It must be located in loft above scen- 
ery, and be installed in a suitable iron box with a tight self- 
closing door. 

Such dampers must be controlled by at least two standard 
single pole switches mounted within approved iron boxes pro- 
vided with self-closing doors without lock or latch, and lo- 
cated, one at the electrician's station and others as designated 
by the Inspection Department having jurisdiction. 

The dampers referred to are ventilators arranged above 
the stage and scenery. In case of fire it is essential that 
these be opened immediately to allow smoke to escape and 
also to prevent the total consumption of oxygen in the 
building by the flames. This rapid consumption of oxygen, 
making it very difficult for people to breathe, thereby caus- 
ing frantic efforts at inhalation, which result in inhaling 
large quantities of smoke and overheated air, is perhaps 
the main cause of the enormous death loss usual in theater 
fires. 

Where current is obtained from an isolated plant which 
is shut down at night time and is not supplied with storage 
battery, or where alternating current is used, it is generally 
more satisfactory to use battery current for the operation 
of the damper, gravity cells being used for this purpose. 
Where the installation is supplied by a direct current system 
which is continuous the damper circuit may be taken directly 
from the system. Figure 148 shows an inexpensive form of 
damper control which is supplied by current from two or 



LOW-POTENTIAL SYSTEMS. 



253 



three cells of gravity battery. The lever arms are made from 
bar iron formed in the shapes shown. The magnet is of 
the type used in door openers and is enclosed in an iron box, 
that part of the enclosure immediately surrounding the mag- 
net pole pieces being of brass. When the circuit is opened 
the armature falls and strikes the lower arm a sharp blow, 
thus releasing the damper rope. To close the damper the cir- 
cuit is first closed, the magnet armature is pulled back in 



s — 1 




Figure 148. 



place by the cord attached to the lower end of it, and the 
damper is closed, the ball in the damper rope engaging in the 
slot in the end of the lever arm. 

/. Dressing Rooms. 

Must be wired in approved conduit or armored cable. All 
pendant lights must be equipped with approved reinforced 
cord, armored cable, or steel armored flexible cord. 

All lamps must be provided with approved guards. 

Experience has proven it a difficult matter to arrange 
dressing rooms in such a way that actors cannot disarrange 



254 MODERN ELECTRICAL CONSTRUCTION. 

them and thus cause troubles of many kinds. One of the 
principal preventive devices is a lamp guard fastened to each 
socket in such a way that it cannot be removed without assist- 
ance from the house electrician. This will prevent the re- 
moval of the lamp and the substitution of a lamp of greater 
candle power or of the portable devices which many actors 
carry that require much more current. A lamp guard so 
arranged that it can be locked on will readily accomplish the 
purpose and such lamp guards are on the market. 

The principal use of light in the dressing rooms is for 
the "make-up" of the actors. One light on each side of every 
mirror, suitably placed, with one or two lights for general 
illumination, are generally sufficient. A receptacle for curl- 
ing iron connection can also be provided, but should also be 
under lock and key. 

Dressing room circuits should be very lightly fused so 
that the use of electric irons will surely blow fuse. 

k. Portable Equipment. • 

Arc lamps used for stage effects must conform to the fol- 
lowing requirements : — 

i. Must be constructed entirely of metal except where 
the use of approved insulating material is necessary. 

2. Must be substantially constructed, and so designed as 
to provide for proper ventilation, and to prevent sparks be- 
ing emitted from lamps when same are in operation, and mica 
must be used for frame insulation. 

3. Front opening must be provided with a self-closing 
hinged door frame, in which wire gauze or glass must be in- 
serted, except in the case of lens lamps, where the front may 
be stationary, and a solid door be provided on back or side. 

4. Must be so constructed that neither carbons nor live 
parts will be brought into contact with metal of hood during 
operation, and arc lamp frames and standards must be so in- 
stalled and protected as to prevent the liability of their being 
grounded. 



LOW-POTENTIAL SYSTEMS. 



255 



5. Switch on standard must be so constructed that acci- 
dental contact with any live portion of same will be impossible. 





Figure 149. 



Figure 150. 



6. All stranded connections in lamp and at switch and 
rheostat must be provided with approved lugs. 

7. Rheostats must be plainly marked with their rated ca- 
pacity in volts and amperes, and, if mounted on standard, 



256 



MODERN ELECTRICAL CONSTRUCTION. 



/ 



s 




/ 

Rheostat No. 83. 

Hardline — One lamp on 220 
volts, 20 amperes. 
Dotted line — One lamp on 
110 volts, 30 amperes. 



V- 



930. 



.CSX. ..£&- 



G&-. -C3P- 




Rheostat No. 82. 

One lamp on 110 volts, 
60 amperes. 




Rheostat No. 83. 

Two lamps on 110 volts 
each, 15 amperes. 



Rheostat No. 82. 

Hard line— Two lamps on 220 volts 
each, 20 amperes. 
Dotted line — Two lamps on 110 
volts each, 30 amperes. 




Rheostat No. 82. 

One lamp on 223 volts, 
35 amperes. 












Rheostat No. 82. 

One lamp on 450 volts, 
20 amperes. 







* 







Rheostat No. 81. 

One lamp on 550 volts, 22 amperes. 

Figure 151. 



LOW-POTENTIAL SYSTEMS. 257 

must be raised to a height of at least three inches above floor. 
Resistance must be enclosed in a substantial and properly 
ventilated metal case which affords a clearance of at least 
one inch between case and resistance element. 

8. A competent operator must be in charge of each arc 
lamp, except that one operator may have charge of two lamps 
when they are not more than ten feet apart, and are so lo- 
cated that he can properly watch and care for both lamps. 

On the stage hand-feed arc lamps are used almost ex- 
clusively and an operator is always required to look after 
the lamps. The style of lamps generally used are shown 
in Figures 149 and 150. Figure 149 shows the focusing or 
spot lamp and Figure 150 the open box or olive lamp, which 
is used for general illumination. These arc lamps require a 
current of from 20 to 40 amperes and should be wired for 
accordingly. 

Figure 151 shows diagrammatically a very useful form of 
rheostat for stage purposes. As most "shows" are constantly 
traveling, the apparatus carried by them should be adjustable 
in so far as voltage is concerned and also as to system, i. e., 
alternating or direct current. As will be seen from the fig- 
ure, this rheostat lends itself to any voltage or system. This 
particular rheostat is manufactured by the Chicago Stage 
Lighting Co. 

/. Bunches. 

Must be substantially constructed of metal and must not 
contain any exposed wiring. 

The cable feeding same must be bushed in an approved 
manner where passing through the metal, and must be prop- 
erly secured to prevent any mechanical strain from coming 
on the connection. 

The bunch light is used in various locations around the 
stage where only a small amount of illumination is required. 



258 MODERN ELECTRICAL CONSTRUCTION. 

Bunches containing 200 32 c. p. lamps have been tried 
but none of them can equal the illumination obtained from 
arc lamps. 

m. Strips. 

Must be constructed of steel of a thickness not less than 
No. 20 U. S. Sheet Metal gage, treated to prevent oxidation, 
and suitably stayed and supported and so designed that flanges 
will protect lamps. 

Cable must be bushed in a suitable manner where passing 
through the metal, and must be properly secured to prevent 
serious mechanical strain from coming on the connections. 

Must be wired in approved conduit or armored cable, each 
lamp receptacle being enclosed within an approved outlet box, 
or the lamp receptacles may be mounted in an iron or steel 
box, metal to be of a thickness, not less than No. 20 U. S. 
Sheet Metal gage, treated to prevent oxidation, so constructed 
as to enclose all wires. Wires to be soldered to lugs of 
receptacles. 

Strip lights are laid on the floor and hung on the scenery 
and are used to illuminate those parts of the scenery where 
the lights from the foots and borders are obstructed. Any of 
the forms shown in Figure 138 may be used for footlight 
construction. Reflectors are generally provided which serve 
to concentrate the light on the spot desired and to protect 
the lamps from accidental contact. Special care must be 
given to cables, where they leave strips; being portable, they 
soon suffer damage at these points. 

n. Portable Plugging Boxes. 

Must be constructed so that no current carrying part will 
be exposed, and each receptacle must be protected by ap- 
proved fuses mounted on slate or marble bases and enclosed 
in a fireproof cabinet equipped with self-closing doors. Each 
receptacle must be constructed to carry thirty amperes with- 
out undue heating, and the bus-bars must have a carrying 
capacity equivalent to the current required for the total num- 



LOW-POTENTIAL SYSTEMS. 



259 



ber of receptacles, and approved lugs must be provided for 
the connection of the master cable. 

When a number of pieces of electrical apparatus are to be 
used at one time on the stage, instead of earring a separate 




Figure 152. 



cable from each piece of apparatus to a pocket, a portable 
plugging box or "spider box" is used. This is shown in Fig- 
ure 152. One large cable is carried from the plugging box to 
a pocket or other convenient point of connection and the 
various pieces of apparatus connected to the plugging box by 
plugs and short cables. This greatly reduces the amount of 
cable used and allows of rapid assembly and removal. 



260 



MODERN ELECTRICAL CONSTRUCTION. 



o. Pin Plug Connectors. 

Must be of an approved type, so installed that the "fe- 
male" part of plug will be on live end of cable, and must 
be so constructed that tension on the cable will not cause 
serious mechanical strain on the connections. 

p. Portable Conductors. 

Flexible conductors used from receptacles to arc lamps, 
bunches and other portable equipments must be approved 




Figure 153. 



stage cable except that for the purpose of feeding a stand 
lamp under conditions where conductors are not liable to 
severe mechanical injury, an approved reinforced cord may 
be used, provided cut-out designed to protect same is not 
fused over six amperes capacity. 

q. Lights on Scenery. 

Where brackets are used they must be wired entirely on 
the inside, fixture stem must come through to the back of the 
scenery and end of stem be properly bushed. 



LOW-POTENTIAL SYSTEMS. 26 1 

The usual method of complying with this rule is shown in 
Figure 153. Everything about the bracket is of metal and 
stage cable is used to make the connection to the outside. 

r. String or Festooned Lights. 

Wiring of same must be of approved type, joints to be 
properly made, soldered and taped, and staggered where 
practicable. 

Where lamps are used in lanterns or similar devices, ap- 
proved guards must be employed. 

A good method of making tap joints in festoons is shown 
in Figure 154. The joints are made staggering and properly 



Figure 154. 

soldered and taped with both rubber and friction taps. The 
cable which is tapped on is then carried along the main cable 
for three or four inches and securely taped. This removes 
nearly all the strain from the joints and prevents the wires 
from working loose. 

s. Special Electrical Effects. 

Where devices are used for producing special effects such 
as lightning, waterfalls, etc., the apparatus must be so con- 
structed and located that flames, sparks, etc., resulting from 
the operation cannot come in contact with combustible 
material. 



262 MODERN ELECTRICAL CONSTRUCTION. 

The necessity for electrical current in connection with 
stage effects has of late years been greatly reduced. Scenes 
and effects of almost any description can be produced by 
means of transparent films attached to and rotating in front 
of an arc lamp. Celluloid films, if they remain stationary ex- 
posed to the light of an arc lamp, may be ignited in two or 
three seconds and burn very rapidly. Gelatine is therefore 
always used. 

Care must be exercised in the use of some of these effects, 
as the sudden and unexpected production of a fire effect or 
of a puff of smoke or momentary blaze such as would be 
produced by a short circuit might have a* disastrous effect 
on the audience. 

In Figure 155 a device is shown for producing lightning 
flashes. It consists of a solenoid, the core of which is at- 
tached to a lever fitted with a piece of carbon. The carbon 
rests on a piece of steel bar. When the circuit is closed the 
solenoid operates and raises the carbon from the piece of steel, 
a considerable flash resulting. The carbon continues to rise 
until the circuit opens, when it drops again, causing an- 
other flash, etc. 

t. Auditorium. 

All wiring must be installed in approved conduit, metal 
moulding or armored cable. 

Exit lights must not have more than one set of fuses be- 
tween same and service fuses. 

Exit lights and all lights in halls, corridors or any other 
part of the building used by audience, except the general au- 
ditorium lighting, must be fed independently of the stage 
lighting, and must be controlled only from the lobby or other 
convenient place in front of the house. All fuses must be 
enclosed in approved cabinets. 

The only fuses allowed on the exit light circuits are the 
branch fuses and the fuses at the service. This necessitates 



LOW-POTENTIAL SYSTEMS. 



running the exit light main direct to the service, not chang- 
ing size and not tapping onto any other main unless both 
mains are of equal carrying capacity. 

All sockets used on the exit and emergency lighting should 




Figure 155. 

be of the keyless type, so that they cannot be controlled from 
any point except the lobby. 

u. Moving Picture Equipments. 

i. Arc Lamp Used as a Part of a Moving Picture Ma- 
chine. — Must be constructed, so far as practicable, similar to 
arc lamps of theatres, and wiring to same must not be of 
less capacity than No. 6 B. & S. gage. 

In the typical moving picture house it is customary, where 
three wire service exists, to balance the arc lamp used for 
the picture machine against the incandescent lights used in 
house about as illustrated in Figure 156. It is a wise precau- 



264 



MODERN ELECTRICAL CONSTRUCTION. 



tion to make connections to the arc as shown in the figure, 
placing the rheostat between the arc and the neutral wire. If 
this precaution is observed the operator will not be so likely 
to receive a shock when working on rheostat while it is alive. 
There will also be less liability of short circuits or trouble on 
the wiring between arc lamp and rheostat of which there is 
usually considerable. The asbestos wire entering arc lamp is 
likely to burn off at arc terminal perhaps, once per week and 




Figure 156. 



operators are prone to carry as much slack on this as they 
dare. 

2. Rheostats. — Must conform to rheostat requirements for 
theatre arcs. 

3. Top and Bottom Reels. — Must be enclosed in steel 
boxes or magazines, each with an opening of approved con- 
struction at bottom or top, so arranged as not to permit en- 
trance of flame to magazine. No solder is to be used in the 
construction of these magazines. The front side of each mag- 
azine must consist of a door spring-hinged and swinging hori- 
zontally, and be provided with a substantial latch. 

The opening referred to that will not permit entrance of 
flame to magazine consists generally of two or more small roll- 
ers between which the film moves. These fit quite closely to- 
gether and if well made and adjusted will not permit any fire 
to get by. Some of these as an additional precaution (which 



LOW-POTENTIAL SYSTEMS. 265 

is much to be recommended) have in addition to the rollers 
a narrow tube of about VA inches in length through which 
the film is drawn. It has by repeated experiments been found 
impossible to draw a flaming piece of film through this 
aperture. 

The two provisions of the rule concerning the door to the 
magazine do not seem to be of the wisest. Close observa- 
tion of numerous operators at work reveals the fact that they 
are nearly all give to opening their magazines a little while 
before finishing a picture so as to be ready for a quick change 
of film. When the change of film is made they have the 
habit of resuming the run without stopping to close the doors 
at once and afterward forgetting about it. A spring hinge on 
door would naturally close it but the spring pressing against 
door is very annoying while changing film and threading and 
is therefore often found blocked. The net result of a spring 
hinge is often that the door is permanently blocked open. To 
avoid the unnecessary dangers careless operators subject their 
audiences to, in this way, magazines have been devised in 
which it is difficult or entirely impossible for a film to be run 
off unless the doors are securely locked. 

If such magazines are not to be insisted upon it would 
seem preferable to hinge the door on the side at which the 
fire valves (as the rollers through which the film must pass 
are called) are located. A door arranged in this way and 
tightly fitting against the hinge side of the magazine may 
prevent flames following the film up to the fire valve from get- 
ting around into the magazine even if the door happens to 
be open. 

4. Automatic Shutter. — Must be provided and must be so 
constructed as to shield the film from the beam of light when- 
ever the film is not running at operating speed. Shutter must 
be permanently attached to the gate frame. 



266 MODERN ELECTRICAL CONSTRUCTION 

There are very few shutters in use at the present time 
that depend upon the rnotion of the film for their operation 
as this rule requires. Most of the shutters now in use ad- 
mit light to strike the film when the machine is in motion. 
Some of them only require that the handle be pressed. There 
is, however, no guarantee that the film will be in motion 
whenever the machine is. Many of the old much used films 
have their sprocket holes so badly torn that the film may 
stop dead still even though the machine be running. It also 
happens that pieces of broken film become detached and 
stick at the edge of the light aperture long enough to become 
ignited and thus ignite the rest of the film even though it be 
in motion. Too much reliance must therefore never be 
placed upon any automatic light shutter. The chief re- 
liance should always be in the magazines. If these are in 
good order and if all films in booth are well enclosed there 
can be no serious fire ; it will be limited to a few feet of film 
between the upper and lower magazine. 

5. Extra Films. — Must be kept in individual metal boxes 
equipped with tight-fitting covers. 

This is a good rule and very few serious fires would result 
if it were rigidly obeyed. The rule could be improved by 
requiring that all of these individual boxes be kept in one 
place or within one box provided with well fitting cover ar- 
ranged in some way that it cannot accidentally be left open. 
The operator is often hurried by manager to make change as 
rapidly as possible and neglects for the moment to close 
the box meaning to do so later and later often forgets. 

The films should all be in one place because the chances 
of accidental ignition by careless use of matches, etc., are 
thereby reduced. Experience has shown that nearly always 
when one roll of film burns in a booth it sets fire to all the 



LOW-POTENTIAL SYSTEMS. 267 

rest. This is probably due to the fact that the operator who 
is careless enough to let one roll ignite is also careless enough 
to leave all of his film lying about open. 

6. Machine Operation. — Must be operated by hand. (Mo- 
tor driven will not be permitted.) 

The only reason for this rule is the fear that an operator 
would not pay close enough attention to the machine. Be- 
ing compelled to operate by hand he must of course stay with 
the machine while otherwise he might be in a side room smok- 
ing or reading. There are moving picture machines which 
cannot be operated by hand and in connection with these the 
rule is generally ignored. 

7. Machine Enclosure. — Machine must be placed in an 
enclosure or house made of suitable fireproof material ; must 
be properly ventilated, properly lighted and large enough for 
operator to walk freely on either side of or back of machine. 
All openings into this booth must be arranged so as to be en- 
tirely closed by doors or shutters constructed of the same or 
equally good fire-resisting material as the booth itself. Doors 
or covers must be arranged so as to be held normally closed 
by spring hinges or equivalent devices. 

The general lay out of a typical moving picture booth of 
the larger kind is given in Figure 157. In this booth are 
shown 2 moving picture machines; one stereoptican and one 
spot light. There is generally plenty of room available cross- 
wise of the building but it is very desirable to limit the room 
lengthwise of the auditorium as much as possible on account 
of the seating capacity . Many of the booths have no other 
entrance but a trap door with a ladder leading into it. Such 
an arrangement is almost criminal. Film burns very rapidly 
and the gases are very poisonous and every possible facility 
should be given an operator to get away. The booth should 
be provided with a door on the side on which the cranks of 



268 



MODERN ELECTRICAL CONSTRUCTION. 



machines are located so that it will be unnecessary for opera- 
tor to pass around a burning film or that the likelihood of a 
burning film being located between himself and the door be 
reduced to a minimum. 

The door to booth should be made to swing outward and 
be provided with spring hinges so that it will close itself. It 




Figure 157. 



should open upon a platform level with the floor of booth 
so as to facilitate the "get away" of the operator as much as 
possible. It is true that most of the fires that occur in con- 
nection with moving pictures machines are due to the care- 
lessness of operators, but much of this carelessness is super- 
induced by the awkward conditions under which some of them 
are required to work. Many of them are today working in 
booths in which it is necessary to crawl on hands and knees 
to get about. The door should preferably be kept closed but 
on account of the heated conditions existing in most booths 
it would be found impossible to enforce such a rule. It will 



LOW-POTENTIAL SYSTEMS. 269 

be well enough if arrangements are such that the door can be 
readily closed when a fire actually occurs. The door could 
to advantage be connected with the shutters in such a manner 
that closing the door would close the shutters. This would 
cause the shutters to be worked after each show and thus 
tend to keep them in working order. 

The house should have a large vent communicating with 
the outside air in the ceiling and in order to make proper 
ventilation possible, there should be openings along bottom of 
booth. These openings to be covered by fine and strong wire 
mesh. Nearly all booths are sooner or later provided with 
fan motors and such a motor might as well be provided and 
placed so that it will exhaust air through the booth from the 
auditorium. 

The wiring necessary to be introduced into the booth 
should be run along the ceiling in conduit to point directly 
above arc lamps so as to reduce amount of loose wire as 
much as possible. As the ends of wire connecting to arc 
lamp become very hot and in consequence must be often re- 
connected it is customary to install them of such a length 
that there may be considerable slack. This should be neatly 
coiled up near the ceiling. 

The floor of booth should be arranged to be clear of 
everything. Take up magazines become deranged in one 
way or another quite frequently and in such a case there is 
likely to be much film run onto the floor. Many operators are 
careless enough to finish a show by running onto floor in 
such cases. When such an accident occurs there is likely to 
be a bad tangle of film and the less there is in the way on the 
floor the better it will be for all concerned. Any operator 
who has once had the experience of trying to straighten out 
a mess of film and get it back upon the reel while an impatient 
audience was clapping and calling to him to go on will ap- 
preciate this point. 



270 



MODERN ELECTRICAL CONSTRUCTION. 



The rheostat if placed within the booth is best suspended 
a foot or so from the ceiling wherever the height of booth 
will permit. If placed upon a shelf, rubbish is likely to be 
stored close to it. 

There must be either two or three openings in booth for 
each moving picture machine. One of these is the "peek 
hole" through which the operator must view his picture, an- 




Figure 158. 



other for the projection of the picture and generally a third 
through which the arc lamp may be used in connection with 
lantern slides. The two last mentioned openings may be very 
small, in fact, there are a number of booths which have no 
opening at all a funnel having been built which encloses the 
Beam of light from the projecting lens until it passes out of 
the house. The "peek hole" may be closed with glass, wire 
glass being preferred. 

The main care should be to keep the audience from dis- 



LOW-POTENTIAL SYSTEMS. 



271 



covering that there is a fire. In a properly arranged and ven- 
tilated booth the film will be burned in a few seconds and 
no further harm will be done unless the audience become 
frightened. 

Where openings exist they must be provided with shut- 
ters by which they can be instantly closed in case of fire. The 
great majority of such shutters are arranged in guides as 
shown in Figure 158 and depend upon gravity to close them 
when the supports are released. A sliding shutter is pref- 
erable because a swinging shutter is more apt to meet with 




Figure 159. 



obstructions in a crowded booth. A sliding shutter may be 
equipped with springs to help pull it down if desired. The 
guides for these shutters should be long enough so that the 
shutter will remain with its full length encased in them 
when open. The shutter should also be of a greater height 
than width. If it is wider than its height there is great pos- 
sibility that it may hang a little lower on one side than on the 
other and become wedged in sliding down. Many booths are 
made up of thin metal. If shutters are placed upon such 
walls the guides should be strong enough to form substantial 
braces that will not easily bend and cause the shutter to stick. 



2*] 2 MODERN ELECTRICAL CONSTRUCTION. 

Figure 159 shows an inside view of a booth and the ar- 
rangement of strings by which they are held open. The main 
string which supports all of them passes over the top of 
each machine and traverses the whole length of the booth. No 
matter in what portion a film may burn it will soon destroy 
the string and drop all of the shutters. As the string termi- 
nates at the door it is convenient for any one to release it 
when leaving the booth perhaps before the fire has reached 
the string. Fusible links of the proper kind in series with the 
string will be an improvement. 

8. Reels Containing Films Under Examination or in 
Process of Rewinding. — Must be enclosed in magazines or ap- 
proved metal boxes similar to those required for films in 
operation, and not more than two feet of film shall be ex- 
posed in booth. 

This is one of the most important rules. Operators are 
very much in the habit of rewinding while operating and this 
is of course dangerous practice. As with the reels on ma- 
chine so here it is of great importance to obtain magazines 
that cannot be operated with doors open. This will at least 
compel operators to keep films enclosed. Rewinding on open 
reel while operating machine means that film will be open in 
booth during the whole run of picture. 

Before placing a new outfit in commission a thorough test 
as to its fireproof qualities should be made. Some old pieces 
of film should be procured and attempts made to work pieces 
•of burning film through the five valves. No magazine in 
which this is possible should be used. 

Next a piece of film should be threaded into the machine 
in its proper place and the light, strongly concentrated and 
with the strongest current ever used (50 to 60 amperes) al- 
lowed to strike as much of the light shutter and other parts 
of frame that may be within the possible range of focused 
light. The light should be left on each such place for a con- 



LOW-POTENTIAL SYSTEMS. 2J1> 

siderable time so that one feels assured that the film cannot 
be ignited in this way. If it is possible to ignite film in this 
manner the machine should be altered to make this impossible. 

39. Outline Lighting. 

Wiring (Other than Signs on Exterior of Bindings) : — 

a. Must be connected only to low-potential systems. 

b. Open or conduit work may be used, but moulding will 
not be permitted. 

c. For open work, wires must have an approved rubber 
insulating covering. Must be rigidly supported on non-com- 
bustible, non-absorptive insulators,, which separate the wires 
at least one inch from the surface wired over, and must be 
kept apart at least two and one-half inches for voltages up 
to 300, and four inches for higher voltages. 

Rigid supporting requires, under ordinary conditions where 
wiring over flat surfaces, supports at least every four, and 
one-half feet. If the wires are liable to be disturbed, the 
distances between supports should be shortened. 

d. Where flexible tubing is required, the ends must be 
sealed and painted with moisture repellant, and kept at least 
one-half inch from surface wired over. 

e. Wires for use in rigid or flexible steel conduit must 
comply with requirements for unlined conduit work. Where 
armored cable is used, the conductors must be protected from 
moisture by lead sheath between armor and insulation. 

/. Must be protected by its own cut-out, and controlled 
by its own switch. Cut-outs, switches, time switches, flash- 
ers and similar appliances, must be of approved design, and 
must, if located inside the building, be installed as required 
by the code for such devices. If outside the building they 
must be inclosed in a steel or cast-iron box. 

If a steel box is used, the minimum thickness of the steel 
must be 0.125 of an inch (No. 11 U. S. gage). 

g. Boxes must be so constructed that when switch oper- 
ates the blade shall clear the door by at least one inch, and 
they must be moisture proof. 

h. Circuits must be so arranged that not more than 



274 



MODERN ELECTRICAL CONSTRUCTION. 



1,320 watts will be finally dependent upon a single cut-out; 
nor shall more than 66 sockets or receptacles be connected 
to single circuit. 

*. Sockets and receptacles must be of the keyless porce- 
lain type, and wires must be soldered to lugs on same. 

Wiring for outline lighting is done either in conduit, ar- 
mored cable or open work. If conduit is used the whole in- 
stallation should be made watertight. Only such fittings 
should be used as are provided for threaded joints. The or- 
dinary outlet box with locknut and bushing should never be 




Figure 100. 



Figure 161. 



used for this purpose. If armored cable is used the wires 
must be covered by a lead sheath and watertight boxes must 
be used at outlets. 

The cheapest construction consists of porcelain receptacles 
and open wiring. Rubber covered wire and receptacles which 
give a spacing of one inch from the surface wired over must 
be used. Receptacles designed for this use are shown in Fig- 
ures 160 and 161. It will be noted that the wires are raised 
some distance from the surface on which it is placed to give 
the required one inch spacing. 

All wires must be soldered to the binding posts of re- 



LOW-POTENTIAL SYSTEMS. 275 

ceptacles. This is required as the ordinary handling of the 
wire when installing is liable to loosen the wire from the 
binding posts if it is not soldered. 

40. Car Wiring and Equipment of Cars. 
a. Protection of Car Body, etc. 

1. Under side of car bodies to rje protected by approved 
fire-resisting, insulating material, not less than one-eighth 
inch in thickness, or by sheet iron or steel, not less than .04 
inch in thickness, as specified in Section a 2, 3 and 4. This 
protection to be provided over all electrical apparatus, such 
as motors with a capacity of over 75 H. P. each, resistances, 
contactors, lightning arresters, air-brake motors, etc., and also 
where wires are run, except that protection may be omitted 
over wires designed to carry 25 amperes or less if they are 
encased in metal conduit. 

2. At motors of over 75 H. P. each, fire-resisting material 
or sheet iron or steel to extend not less than 8 inches beyond 
all edges of openings in motors, and not less than 6 inches 
beyond motor leads on all sides. 

3. Over resistances, contactors and lightning arresters, 
and other electrical apparatus, excepting when amply pro- 
tected by their casing, fire-resisting material or sheet iron 
or steel to extend not less than 8 inches beyond all edges of 
the devices. 

4. Over conductors, not encased in conduit, and con- 
ductors in conduit when designed to carry over 25 amperes, 
unless the conduit is so supported as to give not less than 
one-half inch clear air space between the conduit and the 
car, fire-resisting material or sheet iron or steel to extend 
at least 6 inches beyond conductors on either side. 

The fire-resisting, insulating material or sheet iron or steel 
may be omitted over cables made up of flameproof braided 
outer covering when surrounded by one-eighth inch flame- 
proof covering, as called for by Section i, 4. 

5. In all cases fireproof material or sheet iron or steel 
to have joints well fitted, to be securely fastened to the sills, 
floor timbers and cross braces, and to have the whole surface 
treated with a waterproof paint. 



276 MODERN ELECTRICAL CONSTRUCTION. 

6. Cut-out and switch cabinets to be substantially made 
of hard wood. The entire inside of cabinet to be lined with 
not less than one-eighth inch fire-resisting, insulating ma- 
terial which shall be securely fastened to the woodwork, and 
after the fire-resisting material is in place the inside of the 
cabinet shall be treated with a waterproof paint. 
b. Wires, Cables, etc. 

1. All conductors to be stranded, the allowable carrying 
capacity being determined by Table "A" of No. 18, except 
that motor, trolley and resistance leads shall not be less than 
No. 7 B. & S. gage, heater circuits not less than No. 12 B. & 
S. gage, and lighting and other auxiliary circuits not less than 
No. 14 B. & S. gage. 

The current used in determining the size of motor, trolley 
and resistance leads shall be the per cent of the full load cur- 
rent, based on one hour's run of the motor, as given by the 
following table : — 

Size each Motor 

Motor. Leads. 

75 H. P. or less 50% 

Over 75 H. P. 4 5% 

Approved fixture wire will be permitted for wiring ap- 
proved clusters. 

2. To have an insulation and braid approved for wires 
carrying currents of the same potential. 

3. When run in metal conduit, to be protected by an 
additional braid. 

Where conductors are laid in conduit, not being drawn 
through, the additional braid will not be required. 

4. When not in conduit, in approved moulding, or in 
cables surrounded by one-eighth inch flame-proof covering, 
must be approved rubber covered (except that tape may be 
substituted for braid) and be protected by an additional flame- 
proof braid, at least one thirty-second inch in thickness, the 
outside being saturated with a preservative flame-proof com- 
pound, except that when motors are so enclosed that flame 
cannot extend outside of the casing, the flame-proof covering 
will not be required on the motor leads. 

5. Must be so spliced or joined as to be both mechanically 



Trolley 


Resistance 


Leads. 


Leads. 


40% 


15% 


35% 


15% 



LOW-POTENTIAL SYSTEMS. 277 

and electrically secure without solder. The joints must then 
be soldered and covered with an insulation equal to that on 
the conductors. 

Joints made with approved splicing devices and those con- 
necting the leads at motors, plows or third rail shoes need 
not be soldered. 

6. All connections of cables to cut-outs, switches and fit- 
tings, except those to controller connection boards, when de- 
signed to carry over 25 amperes, must be provided with lugs 
or terminals soldered to the cable, and securely fastened to 
the device, by bolts, screws or by clamping; or, the end of 
the cable, after the insulation is removed, shall be dipped in 
solder and be fastened into the device by at least two set 
screws having check nuts. 

All connections for conductors to fittings, etc., designed to 
carry less than 25 amperes, must be provided with up-turned 
lugs that will grip the conductor between the screw and the 
lug, the screws being provided with flat washers ; or by block 
terminals having two set screws, and the end of the con- 
ductors must be dipped in solder. Soldering, in addition to 
the connection of the binding screws, is strongly recommended, 
and will be insisted on when above requirements are not 
complied with. 

This rule only to apply to circuits where the maximum 
potential is over 25 volts and current exceeds 5 amperes. 

c. Cut-outs, Circuit Breakers and Switches. 

1. All cut-outs and switches having exposed live metal 
parts to be located in cabinets. Cut-outs and switches, not 
in iron boxes or in cabinets, shall be mounted on not less than 
one-fourth inch fire-resisting, insulating material, which shall 
project at least one-half inch beyond all sides of the cut-out 
or switch. 

2. Cut-outs to be of the approved cartridge or approved 
blow-out type. 

3. All switches controlling circuits of over 5 ampere ca- 
pacity shall be of approved single pole, quick break or ap- 
proved magnetic blow-out type. 

Switches controlling circuits of 5 ampere or less capacity 
may be of the approved single pole, double break, snap type/ 



278 MODERN ELECTRICAL CONSTRUCTION. 

4. Circuit breakers to be of approved type. 

5. Circuits must not be fused above their safe carrying 
capacity. 

6. A cut-out must be placed as near as possible to the 
current collector, so that the opening of the fuse in this 
cut-out will cut off all current from the car. 

When cars are operated by metallic return circuits, with 
circuit breakers connected to both sides of the circuit, no fuses 
in addition to the circuit breakers will be required. 

d. Conduit. 

When from the nature of the case, or on account of the size of 
the conductors, the ordinary pipe and junction box construction is 
not permissible, a special form of conduit system may be used, 
provided the general requirements as given below are complied 
with. 

1. Metal conduits, outlet and junction boxes to be con- 
structed in accordance with standard requirements except 
that conduit for lighting circuits need not be over five-six- 
teenths inch internal diameter and one-half inch external di- 
ameter, and for heating and air motor circuits need not be 
over three-eighths inch internal diameter and nine-sixteenths 
inch external diameter, and all conduits where exposed to 
dampness must be water tight. 

2. Must be continuous between and be firmly secured into 
all outlet or junction boxes and fittings, making a thorough 
mechanical and electrical connection between same. 

3. Metal conduits, where they enter all outlet or junction 
boxes and fittings, must be provided with approved bushings 
fitted so as to protect cables from abrasion. 

4. Except as noted in Section i, 2, must have the metal 
of the conduit permanently and effectively grounded. 

5. Junction and outlet boxes must be installed in such a 
manner as to be accessible. 

6. All conduits, outlets or junction boxes and fittings to 
be firmly and substantially fastened to the framework of the 
car. 

e. Moulding. 

1. To consists of a backing and a capping and to be 
constructed of fire-resisting, insulating material, except that 



LOW-POTENTIAL SYSTEMS. 279 

it may be made of hard wood where the circuits which it is 
designed to support are normally not exposed to moisture. 

2. When constructed of fire-resisting; insulating material, 
the backing shall not be less than one-fourth inch in thickness 
and be of a width sufficient to extend not less than i inch 
beyond conductors at sides. 

The capping, to be not less than one-eighth inch in thick- 
ness, shall cover and extend at least three-fourths inch be- 
yond conductors on either side. 

The joints in the moulding shall be mitred to fit close, 
the whole material being firmly secured in place by screws 
or nails, and treated on the inside and outside with a water- 
proof paint. 

When fire-resisting moulding is used over surfaces already 
protected by one-eighth inch fire-resisting, insulating mate- 
rial no backing will be required. 

3. Wooden mouldings must be so constructed as to thor- 
oughly encase the wire and provide a thickness of not less 
than three-eighths inch at the sides and back of the conductors, 
the capping being not less than three-sixteenths inch in thick- 
ness. Must have both outside and inside two coats of water- 
proof paint. 

The backing and the capping shall be secured in place by 
screws. 

/. Lighting and Lighting Circuits. 

1. Each outlet to be provided with an approved receptacle, 
or an approved cluster. No lamp consuming more than 128 
watts to be used. 

2. Curcuits to be run in approved metal conduit, or ap- 
proved moulding. 

3. When metal conduit is used, except for sign lights, all 
outlets to be provided with approved outlet boxes. 

4. At outlet boxes, except where approved clusters are 
used, receptacles to be fastened to the inside of the box, and 
the metal cover to have an insulating bushing around open- 
ing for the lamp. 

When approved clusters are used, the cluster shall be thor- 
oughly insulated from the metal conduit, being mounted on 
a block of hard wood or fire-resisting, insulating material. 



280 MODERN ELECTRICAL CONSTRUCTION. 

5. Where conductors are run in moulding the receptacles 
or cluster to be mounted on blocks of hard wood or of fire- 
proof insulating material. 

g. Heaters and Heating Circuits. 

1. Heaters to be of approved type. 

2. Panel heaters to be so constructed and located that 
when heaters are in place all current-carrying parts will be 
at least 4 inches from all woodwork. 

Heaters for cross seats to be so located that current-carry- 
ing parts will be at least 6 inches below under side of seat, 
unless under side of seat is protected by not less than one- 
fourth inch fire-resisting, insulating material, or .04 inch 
sheet metal with 1 inch air space over same, when the dis- 
tance may be reduced to 3 inches. 

Truss plank heaters to be mounted on not less than one- 
quarter inch fire-resisting, insulating material, the legs or 
supports for the heaters providing an air space of not less 
than one-half inch between the back of the heater and the in- 
sulating material. 

3. Circuits to be run in approved metal conduit, or in ap- 
proved moulding, or if the location of conductors is such as 
will permit an air space of not less than 2 inches on all sides 
except from the surface wired over, they may be supported 
on porcelain knobs or cleats, provided the knobs or cleats are 
mounted on not less than one-fourth inch fire-resisting, in- 
sulating material extending at least 3 inches beyond con- 
ductors at either side, the supports raising the conductors not 
less than one-half inch from the surface wired over, and be- 
ing not over 12 inches apart. 

h. Air Pump Motor and Circuits. 

1. Circuits to be run in approved metal conduit or in ap- 
proved moulding, except that when run below the floor of the 
car they may be supported on porcelain knobs or cleats, pro- 
vided the supports raise the conductors at least one-half inch 
from the surface wired over and are not over 12 inches apart. 

2. Automatic control to be enclosed in approved metal 
box. Air pump and motor, when enclosed, to be in approved 



LOW-POTENTIAL SYSTEMS. 28 1 

metal box or a wooden box lined with metal of not less than 
one thirty-second inch in thickness. 

When conductors are run in metal conduit the boxes sur- 
rounding automatic control and air pump and motor may 
serve as outlet boxes. 

i. Main Motor Circuits and Devices. 

1. Conductors connecting between trolley stand and main 
cut-out or circuit breakers in hood to be protected where wires 
enter car to prevent ingress of moisture. 

2. Conductors connecting between third rail shoes on same 
truck, to be supported in an approved fire-resisting, insulating 
moulding, or in approved iron conduit supported by soft rub- 
ber or other approved insulating cleats. 

3. Conductors on the underside of the car, except as noted 
in Section i, 4, to be supported in accordance with one of the 
following methods : — 

a. To be run in approved metal conduit, junction boxes 
being provided where branches in conduit are made, and 
outlet boxes where conductors leave conduit. 

b. To be run in approved fire-resisting, insulating 
moulding. 

c. To be supported by insulating cleats, the supports 
being not over 12 inches apart. 

4. Conductors with flameproof braided outer coverings, 
connecting between controllers at either end of car, or con- 
trollers and contactors, may be run as a cable, provided the 
cable where exposed to the weather is encased in a canvas 
hose or canvas tape, thoroughly taped or sewed at ends and 
where taps from the cable are made, and the hose or tape 
enters the controllers. 

Conductors with or without flameproof braided outer cov- 
ering connecting between controllers at either end of the car, 
or controllers and contactors, may be run as a cable, provided 
the cable throughout its entire length is surrounded by one- 
eighth inch flameproof covering, thoroughly taped or sewed 
at ends, or where taps from cable are made, and the flame- 
proof covering enters the controllers. 

Cables where run below floor of car may be supported by 



2o2 MODERN ELECTRICAL CONSTRUCTION. 

approved insulating straps or cleats. Where run above floor 
of car, to be in a metal conduit or wooden box painted on the 
inside with not less than two coats of flameproof paint, and 
where this box is so placed that it is exposed to water, as by 
washing of the car floor, attention should be given to making 
the box reasonably waterproof. 

Canvas hose or tape, or flameproof material surrounding 
cables after conductors are in same, to have not less than two 
coats of waterproof insulating material. 

5. Motors to be so drilled that, on double truck cars, con- 
necting cables can leave motor on side nearest to king bolt. 

6. Resistances to be so located that there will be at least 
6 inch air space between resistances proper and fire-resisting 
material of the car. To be mounted on iron supports, being 
insulated by non-combustible bushings or washers, or the iron 
supports shall have at least 2 inches of insulating surface be- 
tween them and metal work of car, or the resistances may 
be mounted on hard wood bars, supported by iron stirrups, 
which shall have not less than 2 inches of insulating surface 
between foot of resistance and metal stirrup, the entire sur- 
face of the bar being covered with at least one-eighth inch 
fire-resisting, insulating material. 

The insulation of the conductor, for about. 6 inches from 
terminal of the resistance, should be replaced, if any insula- 
tion is necessary, by a porcelain bushing or asbestos sleeve. 

7. Controllers to be raised above platform of car by a 
not less than 1 inch hard wood block, the block being fitted 
and painted to prevent moisture working in between it and 
the platform. 

;. Lightning Arresters. 

1. To be preferably located to protect all auxiliary circuits 
in addition to main motor circuits. 

2. The ground conductor shall be not less than No. 6 B. 
& S. gage, run with as few kinks and bends as possible, and 
be securely grounded. 

k. General Rules. 

1. When passing through floors, conductors or cables must 
be protected by approved insulating bushings, which shall fit 
the conductor or cable as closely as possible. 



LOW-POTENTIAL SYSTEMS. 283 

2. Moulding should never be concealed except where 
readily accessible. Conductors should never be tacked into 
moulding. 

3. Short bends in conductors should be avoided where pos- 
sible. 

4. Sharp edges in conduit or in moulding must be 
smoothed to prevent injury to conductors. 

41. Car Houses. 

a. The trolley wires must be securely supported on in- 
sulating hangers. 

b. The trolley hangers must be placed at such a distance 
apart that, in case of a break in the trolley wire, contact with 
the floor cannot be made. 

c. Must have an emergency cut-out switch located at a 
proper place outside of the building, so that all the trolley 
wires in the building may be cut out at one point, and line 
insulators must be installed, so that when this emergency 
switch is open, the trolley wire will be dead at all points within 
100 feet of the building. The current must be cut out of the 
building when not needed for use in the building. 

This may be done by the emergency switch, or if preferred 
a socond switch may be used that will cut out all current from the 
building, but which need not cut out the trolley wire outside as 
would be the case with the emergency switch. 

d. All lamps and stationary motors must be installed in 
such a way that one main switch may control the whole of 
each installation, lighting and power independently of the 
main cut-out switch called for in Section c. 

e. Where current for lighting and stationary motors is 
from a grounded trolley circuit, the following special rules 
to apply : — 

1. Cut-outs must be placed between the non-grounded 

side and lights or motors they are to protect. No 
set or group of incandescent lamps requiring over 
2,000 watts must be dependent upon one cut-oiit. 

2. Switches must be placed between non-grounded side 

and lights and motors they are to protect. 

3. Must have all rails bonded at each joint with a con- 

ductor having a carrying capacity at least equiva- 
lent to No. o B. & S. gage annealed copper wire, 



284 



MODERN ELECTRICAL CONSTRUCTION. 



and all rails must be connected to the outside 
ground return circuit by a not less than No. o B. & 
S. gage copper wire or by equivalent bonding 
through the track. All lighting and stationary 
motor circuits must be thoroughly and permanently 
connected to the rails or to the wire leading to the 
outside ground return circuit. 

f. All pendant cords and portable conductors will be con- 
sidered as subject to hard usage. 

g. Must, except as provided in Section e, have all wiring 
and apparatus installed in accordance with the rules for con- 
stant-potential systems. 

h. Must not have any system of feeder distribution cen- 
tering in the building. 

i. Cars must not be left with the trolley in electrical con- 
nection with the trolley wire. 

Figure 162 shows the desired layout of switches as called 
for in this rule. Switch 1 when opened will disconnect all 



T 



rr 



Figure 162. 



the trolley wires within 100 feet of the building in either di- 
rection, as well as those in the house. 'If the house only is 
to be disconnected, switch 2 may be used. The broken lines 
indicate feeders run either underground or on poles to carry 
current around the building or supply power for light which 
may be desired to use while the trolley system is dead. The 
small black squares indicate the location of line insulators. 



LOW-POTENTIAL SYSTEMS. 



285 



The above rule fits the car houses in the smaller cities 
better than it does those of large cities. In the latter the car 
house usually consists of a number of bays separated from 
each other by fire walls and constructed entirely of fireproof 
material. There is never anything in these bays that could 
burn with the exception of the cars themselves. It is advis- 
able to arrange each bay with a service switch in addition to 
those called for by the rule. It will then be generally found 
that the main switch need not be used. 

The rule allows the use of single pole switches on lighting 
from grounded trolley circuits. So long as the ground con- 




Figure 163. 



nections are in good condition this is all that is necessary. 
In car houses, etc., where it is most likely that such method 
of lighting will be used the rails are generally relied upon to 
furnish at least part of the ground connection. These rails 
are often taken up or disconnected so that the breaking of 
the ground connection is always a possibility. 

Referring to Figure 163, should such a break or bad con- 
dition exist at A and the group of lights at the right be 
turned on, a man working on the group of lights at the 
left might be severely injured even though the switch was dis- 
connected. 



286 



MODERN ELECTRICAL CONSTRUCTION. 



Regarding the relative position of switch and fuses it will 
be noticed that the rule does not forbid the placing of the 
switch ahead of the fuses. Owing to the high potential gen- 
erally used with trolley lines, and the fact that the switches 
and fuses are often handled by men who do not fully realize 
the life hazard, it is well to install the switch so that the fuse 
terminals will be dead when the switch is open. 

As a curious illustration of what may sometimes occur 
from imperfect grounding the particulars of a recent electrical 
fire may be interesting. In a railway station, which was partly 
of metal and directly connected to a bridge crossing a trolley 




Figure 164. 



line, there had been considerable annoyance from so-called 
"static" discharges for which no cause could be found. One 
of these discharges resulted in piercing a gas pipe and start- 
ing a fire. On investigation the conditions indicated diagram- 
matically in Figure 164 were found to exist and the cause of 
the fire determined. 

The trolley passed under the metal work of the viaduct 
and within about one foot of the iron beams of the struc- 
ture. The conditions were such that very frequently the 
trolley wheel would leave the trolley wire and immediately 
make contact with the metal of the structure above. This fact 
was evidenced by the presence of many burns on the metal 
work. 

As a matter of fact the trolley wheel before coming in 



LOW-POTENTIAL SYSTEMS. 2&] 

contact with the metal structure of the viaduct was discon- 
nected from the current supply and, consequently, no current 
could have come from this source. But it must be borne in 
mind that the motor, at the moment of disconnection, be- 
comes a generator and its fields are fully charged. The dis- 
charge of the fields induces an enormous voltage in the motor 
windings and this passes to the structure, which was poorly 
grounded, and finds a path to ground through the gas pipe 
previously mentioned finally piercing this pipe and starting 
the fire. Connecting the structure and the piping system by 
a suitable wire, as shown by broken lines in the figure, elimi- 
nated the trouble. 

42. Lighting and Power from Railway Wires. 

a. Must not be permitted, under any pretence, in the 
same circuit with trolley wires with a ground return, except 
in electric railway cars, electric car houses, power houses, pas- 
senger and freight stations connected with the operation of 
electric railways. 

The use of the ordinary 550 volt trolley circuits for either 
lighting or power is a hazard. It is permitted only in the 
buildings belonging to the railway companies and it is ques- 
tionable whether it should even be allowed there. There is 
not only a fire hazard but it is unsafe to life. A contact 
with any of these .circuits while a person is standing on the 
ground will result in a severe shock if not in a fatality. In- 
stallations on systems of this type should be given careful 
consideration and all possible protections provided. 

43. Electric Cranes. 

All wiring, apparatus, etc., not specifically covered by special 
rules herein given, must conform to the Standard Rules 
and Requirements of the National Electrical Code, except 
that the switch required by No. 8 c for each motor may be 
omitted. 

a. Wiring. 

1. All wires except bare collector wires, those between 
resistances and contact plates of rheostats and those subjected 



288 MODERN ELECTRICAL CONSTRUCTION. 

to severe external heat, must be approved, rubber-covered 
and not smaller in size than No. 12 B. & S. Insulation on 
wires between resistances and contact plates of rheostats must 
conform to Section d, while wires subjected to severe external 
heat must have approved slow-burning insulation. 

2. All wires excepting collector wires and those run in 
metal conduit or approved flexible cable must be supported 
by knobs or cleats which separate them at least one inch from 
the surface wired over, but in dry places where space is lim- 
ited and the distance between wires as required by Rule 26 h 
cannot be obtained, each wire must be separately encased in 
approved flexible tubing securely fastened in place. 

Collector wires must be supported by approved insulators 
so mounted that even with the extreme movement permitted 
the wires will be separated at all times at least i l / 2 inches from 
the surface wired over. Collector wires must be held at the 
ends by aproved strain insulators. 

3. Main collector wires carried along the runways must 
be rigidly and securely attached to their insulating supports 
at least every 20 'feet, and separated at least 6 inches when run 
in a horizontal plane; if not run in a horizontal plane, they 
must be separated at least 8 inches. If spans longer than 20 
feet are necessary the distance between wires must be in- 
creased proportionately but in no case shall the span exceed 
40 feet. 

4. Where bridge collector wires are over 80 feet long, in- 
sulating supports on which the wires may loosely lie must 
be provided at least every 50 feet. 

Bridge collector wires must be kept at least 2 T A inches 
apart, but a greater spacing should be used whenever it may 
be obtained. 

5. Collector wires must not be smaller in size than speci- 
fied in the following table for the various spans. 

Distance between Size wire 

rigid supports. required. 

Feet. B. & S. 

o to 30 6 

31 to 60 4 

Over 60 2 



LOW-POTENTIAL SYSTEMS. 289 

b. Collectors. 

Must be so designed that sparking between them and col- 
lector wires will be reduced to a minimum. 

c. Switches and Cut-outs. 

1. The main collector wires must be protected by a cut- 
out and the circuit controlled by a switch. Cut-out and switch 
to be so located as to be easy of access from the floor. 

2. Cranes operated from cabs must have a cut-out and 
switch connected into the leads from the main collector wires 
and so located in the cab as to be readily accessible to the 
operator. 

3. Where there is more than one motor on a single crane, 
each motor lead must be protected by a cut-out located in 
the cab if there is one. 

d. Controllers. 

Must be installed according to No. 4, except that if the 
crane is located out doors the insulation on wires between re- 
sistances and contact plates of rheostats must be rubber where 
the wires are exposed to moisture and insulation is necessary 
and also where they are grouped. If the crane operates over 
readily combustible material, the resistance must be placed in 
an enclosure made of non-combustible material, thoroughly 
ventilated and so constructed that it will not permit any flame 
or molten metal to escape in the event of burning out the re- 
sistances. If the resistances are located in the cab, this result 
may be obtained by constructing the cab of non-combustible 
material and providing sides which enclose the cab from its 
floor to a height at least 6 inches above the top of the re- 
sistances. 

e. Grounding of Iron Work. 

The motor frames, the entire frame of the crane and the 
tracks must be permanently and effectually grounded. 

Electric cranes are made in a variety of design and sizes, 

varying from the small crane operated from the ground and 

provided with a single motor, to the larger cranes with four 

or five motors. 



290 MODERN ELECTRICAL CONSTRUCTION. 

The more common form of crane such as is used in large 
shops and other locations where it is necessary to move heavy 
loads consists of an iron bridge elevated some distance and 
carried on wheels which rest on tracks which are supported 
by the building walls or by special steel structures. 

These cranes consist of three principal parts ; the bridge, 
the trolley and the hoist. 

The hoist is operated by a motor geared to a drum and 
is generally the heaviest motor on the crane. 

The bridge motor moves the load in a transverse direction, 
or across the bridge. 

The trolley motor moves the bridge along the runway. 

These motors are controlled from a cab attached to the 
bridge the current being carried to the movable bridge, and 
from the bridge to the hoist motor, by trolley wires fastened 
along the steel work on which rest trolley wheels or shoes. 

The usual processes in the operation of a crane are : the 
hoisting of the load, the movement of the load across the 
bridge and the movement of the bridge and load along the 
runway. The order of these operations may be reversed or 
they may occur together and it is possible to have all motors 
on a crane operating at one time. For this reason, and for 
the further reason that cranes are often overloaded, the wires 
should be of ample size to carry all motors running at one 
time. 

It will be noted that the rule does not require a separate 
switch for each motor. There must be a main switch located 
in the cab (if there is one) which will cut off all motors 
and the starting devices. This switch must be double pole 
for direct current systems and three-pole for three-phase sys- 
tems. There must also be a cut-out for each motor circuit; 
if the crane contains three motors there must be three cut- 



LOW-POTENTIAL SYSTEMS. 2QI 

outs. For direct currents these cut-outs must be double-pole 
and for three-phase systems three-pole. 

There must also be a cut-out and switch located within 
reach from the ground and so arranged that the entire crane 
including trolleys, cab, motor, etc., can be cut dead. 

The rule describes the method of wiring allowed and 
these rules should be closely followed. Open wiring is very 
liable to mechanical injury. Conduit work will often save 
costly interruption of service and is to be recommended. The 
practice of wiring cranes with flexible tubing is not advisable 
for the same reason and for the further reason that it is al- 
most as expensive as conduit work while its life is much 
shorter. 

All collector wires must be supported at the ends by ap- 
proved strain insulators. Insulators such as are shown at 2 
Figure 53 should be used. Porcelain or glass circuit break- 
ers such as shown in Figure 6s should not be used. 

The collector wires are sometimes arranged to be fast- 
ened at each end by -strain insulators and at intermediate 
points rest loosely on insulating supports. This is done to 
allow the use of contact shoes which make contact on the un- 
der side of trolley wires. Such shoes need not be adjustable 
as the free movement of the trolley wire allows for slight 
variations in the travel of the shoe. This construction is not 
in strict accordance with the rule which requires the trolley 
wire to be "rigidly" attached to the insulating supports. It 
is, however, extensively used. Supports as just described 
greatly lessen the tension on the wire, in fact relieve the ten- 
sion just as much as though rigidly supported. The objection 
to this construction lies in the fact that if the trolley wire 
should break it would probably fall to the ground. 

While the steel structure cannot be used as a return for 
the current it is liable at any time to become alive due to 



292 MODERN ELECTRICAL CONSTRUCTION. 

ground on the wiring system and as the structure is liable to 
be insulated from the earth on masonry columns it is very 
essential that it be effectively grounded. 



HIGH-POTENTIAL SYSTEMS. 

550 to 3,500 Volts. 

Any circuit attached to any machine or combination of ma- 
chines which develops a difference of potential between any 
two wires of over 550 volts and less than 3,500 volts, shall 
be considered at a high-potential circuit, and as coming un- 
der that class, unless an approved transforming device is 
used, which cuts the difference of potential down to 550 
volts or less. For 550 volt motor equipments a margin of 
ten per cent above the 550 volt limit will be allowed at the 
generator or transformer without coming under high-po- 
tential systems. 

44. Wires. 

(See also Nos. 16, 17 and 18. For construction rules see Nos. 

49 and 50.) 

a. Must have an approved rubber-insulating covering. 

b. Must be always in plain sight and never encased, ex- 
cept as provided for in No. 8 b, or where required by the In- 
spection Department having jurisdiction. 

c. Must (except as provided for in No. 8&), be rigidly 
supported on glass or porcelain insulators, which raise the wire 
at least one inch from the surface wired over, and must be 
kept about eight inches apart. 

Rigid supporting requires under ordinary conditions, where 
wiring along flat surfaces, supports at least about every four 
and one-half feet. If the wires are unusually liable to be dis- 
turbed, the distance between supports must be shortened. 

In buildings of mill construction, mains of not less than 
No. 8 B. & S. gage, where not liable to be disturbed, may be 
separated about ten inches and run from timber to timber, not 
breaking around, and may be supported at each timber only. 



HIGH-POTENTIAL SYSTEMS. 293 

d. Must be protected on side walls from mechanical injury 
by a substantial boxing, retaining an air space of one inch 
around the conductors, closed at the top (the wires passing 
through bushed holes) and extending not less than seven 
feet from the floor. When crossing floor timbers, in cellars, 
or in rooms where they might be exposed to injury, wires 
must be attached by their insulating supports to the under 
side of a wooden strip not less than one-half an inch in 
thickness. 

With the exception of series arc systems, which are fast 
going out of use, high potential wires are seldom brought 
into buildings. About the only cases where it is necessary 
to bring high tension wires into a building are for motor 
installations, which are provided for in No. 8 b, and instal- 
lations where the transformers are placed inside of the build- 
ing as provided in No. 45. In both of these cases special pre- 
cautions are necessary. 

45. Transformers. (When permitted inside buildings un- 
der No. 14.) 

(See also Nos. 11, 14, 15 and 36. For construction of Trans- 
formers see No. 81.) 

Transformers must not be placed inside of buildings with- 
out special permission from the Inspection Department having 
jurisdiction. 

a. Must be located as near as possible to the point at which 
the primary wires enter the building. 

b. Must be placed in an enclosure constructed of fire-re- 
sisting material ; the enclosure to be used only for this pur- 
pose, and to be kept securely locked, and access to the same 
allowed only to responsible parties. 

c. Must be thoroughly insulated from the ground, or per- 
manently and effectually grounded, and the enclosure in which 
they are placed must be practically air-tight, except that it 
must be thoroughly ventilated to the outdoor air, if possible 
through a chimney or flue. There should be at least six inches 
air space on all sides of the transformer. 



294 MODERN ELECTRICAL CONSTRUCTION. 

The practice of placing transformers inside of buildings 
should be discouraged. It is much better to place them on 
poles or in manholes or specially constructed buildings for 
in these locations they are less liable to be the cause of fatal 
accidents. When placed inside of a building the low potential 
mains should be fused outside of the transformer room and 
the installation should be otherwise arranged to make it un- 
necessary for any one other than an employe of the lighting 
company to ever enter the room and all keys to these rooms 
should be held by the companies employes only. 

In the construction of transformer rooms inside of build- 
ings it is well to provide for proper drainage. A ledge should 
be placed at all door openings of sufficient height to keep 
any oil which might leak out of the transformer from flowing 
into the building. 

The rule allows either grounding or insulating of trans- 
former case. It is generally considered, however, that the 
grounding is preferable as a safeguard to life. With a 
grounded case it is also impossible for a contact to be made 
between the high potential wires and the low potential wires 
through the case. 

46. Series Lamps. 

a. No multiple series or series multiple system of light- 
ing will be approved. 

b. IVust not, under any circumtsances, be attached to gas 
fixtures, 



EXTRA-HIGH-POTENTIAL SYSTEMS. 295 

EXTRA-HIGH-POTENTIAL SYSTEMS. 

Over 3,500 Volts. 

Any circuit attached to any machine or combination of ma- 
chines which develops a difference of potential, between 
any two wires, of over 3,500 volts, shall be considered as 
an extra-high-potential circuit, and as coming under that 
class, unless an approved transforming device is used, which 
cuts the difference of potential down to 3,500 volts or less. 

47. Primary Wires. 

a. Must not be brought into or over buildings, except 
power stations and sub-stations. 

48. Secondary Wires. 

a. Must be installed under rules for high-potential systems 
when their immediate primary wires carry a current at a po- 
tential of over 3,500 volts, unless the primary wires are in- 
stalled in accordance with the requirements as given in No. 
13 or are entirely underground, within city, town and village 
limits. 



NOTICE— DO NOT FAIL TO SEE WHETHER ANY fVULE 
OR ORDINANCE OF YOUR CITY CONFLICTS WITH THESE 
RULES. 



Class D. 



FITTINGS, MATERIALS AND DETAILS OF 
CONSTRUCTION. 



ALL SYSTEMS AND VOLTAGES. 



The following rules are but a partial outline of require- 
ments. Devices or materials which fulfill the conditions of 
these requirements and no more, will not necessarily be accept- 
able. All fittings and materials should be submitted for exam- 
ination and test before being introduced for use. 



Insulated Wires—Rules 49 to 57. 

49. General Rules. 

a. Copper for insulated solid conductors of No. 4 B & S. 
gage and smaller must not vary in diameter more than .002 of 
an inch from the standard. On solid sizes larger than No. 4 
B. & S. gage the diameter shall not vary more than one per 
cent from the specified standard. The conductivity of solid 
conductors shall not be less than 97% of that of pure copper 
of the specified size. 

In all stranded conductors the sum of the circular mils of 
the individual wires, shall not be less than the nominal circu- 
lar mils of the strand by more than one and one-half per cent. 
The conductivity of the individual wires in a strand shall not 



FITTINGS, MATERIALS, ETC. 297 

be less than is given in the following table, which applies to 
tinned conductors : — 

Number. Per cent. 

14 and larger 97.0 

15 96.8 

16 96.6 

17 96.4 

18 96.2 

19 96.0 

20 95.8 

21 95.6 

22 95.4 

23 95.2 

24 95.0 

25 ' 94.8 

26 94.6 

27 94.4 

28 94.2 

29 94.0 

30 93.8 

The Standard for diameters and milages shall be that adopted 
by the American Institute of Electrical Engineers. 

b. Wires and cables of all kinds designed to meet the 
following specifications must have a distinctive marking the 
entire length of the coil so that they may be readily identified 
in the field. They must also be plainly tagged or marked as 
follows : — 

1. The maximum voltage at which the wire is designed 

to be used. 

2. The words "National Electrical Code Standard." 

3. Name of the manufacturing company and, if desired, 

trade name of the wire. 

4. Month and year when manufactured. 

5. The proper type letter for the particular style of wire 

or cable as given for each type of insulation in Nos. 
50 to 57 inclusive. 

Wires described under No. 53 need not have the distinctive mark- 
ings, but are to be tagged. . 

50. Rubber-Covered Wire. 

a. Copper for conductors must be thoroughly tinned. 
Insulation for voltages, to 600 inclusive. 

b. The insulation must consist of a rubber compound, 
homogeneous in character, adhering to the conductor or to the 



298 MODERN ELECTRICAL CONSTRUCTION. 

separator, if one is used, and of a thickness not less than that 
given in the following tables, Sections e and /. 

Measurements of insulating wall are to be made at the thinnest 
portion of the dielectric. 

c. Any one foot sample of completed covering must show 
a dielectric strength sufficient to resist throughout five minutes 
the application of an electro-motive force proportionate to the 
thickness of insulation in accordance with the following 
table :— 

Thickness 
in 64ths inches. 
1 
2 
3 
4 
5 
6 

7 

8 
10 
12 

14 

16 

The source of alternating electro-motive force shall be a 
transformer of at least one kilowatt capacity. The application 
of the electro-motive force shall first be made at 3,000 volts 
for five minutes, then the voltage increased by steps of not 
over 3,000 volts, each held for five minutes, until the rupture 
of the insulation occurs. The tests for dielectric strength 
shall be made on a sample wire which has been immersed in 
water for seventy-two hours. One foot of the wire under 
test is to be submerged in a conducting liquid held in a metal 
trough, one of the transformer terminals being connected to 
the copper of the wire and the other to the metal of the 
trough. 

d. Every length of completed wire or cable must be 
tested after not less than 12 hours immersion in water, and 
while still immersed by the application for one minute of an 
alternating current voltage derived from apparatus of ample 
capacity, the test voltages to be those given in the tables of 
Sections e and /. 



Breakdown 


test 


on 1 foot 




3,000 


volts A. C. 


6,000 


a 


u 


9,000 


a 


u 


11,000 


tt 


n 


13,000 


it 


a 


15,000 


a 


n 


16,500 


it 


n 


18,000 


it 


n 


21,000 


(( 


a 


23,500 


it 


n 


26,000 


n 


a 


28,000 


tt 


(t 



FITTINGS, MATERIALS, ETC. 299 

After this voltage test every length of completed wire or 
cable while still immersed must show an insulation resistance 
after one minute electrification not less than the values given 
in Sections e and /. 

Any length of completed wire or cable may be tested dur- 
ing 30 days immersion in water, and must show not less than 
50 per cent of the insulation resistance required after the 12 
hours' immersion. 

The results of insulation test at different temperatures to 
be reduced to a basis of 60 degrees F. (15.5 degrees C.) by 
using the multipliers in the following table : — 

Temp. Degs. 

Fahr. Multiplier. 

50-52 .69 

53-55 78 

56-58 .88 

59-61 1. 00 

62-64 1. 12 

65-67 1.27 

68-70 1.43 

71-73 1.60 

74-76 1. 8 1 

77-79 2.04 

80-82 2.29 

83-85 2.58 

e. Thickness of insulation, voltage tests and minimum in- 
sulation resistance to be in accordance with the following 
tables. The test voltages are to be for one minute. The 
insulation resistances are after one minute electrification and 
at 60 degrees Fahr. (15.5 C.) 

Tests on Completed Lengths 0-600 Volt Class. 

Type Letters R. S. 
Size 



14 
12 
10 

8 



Thick- Megohms 


per 


Voltage 


s in 64ths mile after 12 


Test one 


inches, hrs. immersion. 


minute. 


3-64 300 




1,500 


3-64 250 




1,500 


3-64 225 




1,500 


3-64 200 




I.500 



30O 



MODERN ELECTRICAL CONSTRUCTION. 



Stze 






Thick- 


Megohms per 


Voltage 








ness in 64ths 


i mile after 12 


Test one 








inchs. 


hrs. immersion. 


minute. 


6 






I-16 


200 


2,000 


4 






I-16 


150 


2,000 


2 






I-16 


125 


2,000 


I 






5-64 


150 


2,500 









5-64 


125 


2,500 


OO 






5-64 


125 


2,500 


ooo 






5-64 


IOO 


2,50O 


0000 






5-64 


100 


2,500 


225,000 


c. 


M. 


3S2 


IOO 


3,000 


300,000 


c. 


M. 


3-32 


IOO 


3,000 


400,000 


C. 


M. 


3-32 


IOO 


3,000 


500,000 


C. 


M. 


3-32 


IOO 


3,000 


600,000 


C. 


M. 


7-64 


IOO 


3,500 


700,000 


C. 


M. 


7-6.-: 


IOO 


3,500 


800,000 


C. 


M. 


7-64 


IOO 


3,500 


900,000 


c. 


M. 


7-64 


IOO 


3,500 


1,000,000 


c. 


M. 


7-64 


IOO 


3,500 


1,250,000 


c. 


M. 


1-8 


IOO 


3,500 


1,500,000 


c. 


M. 


1-8 


75 


3,500 


1,750,000 


c. 


M. 


1-8 


60 


3,500 


2,000,000 


c. 


M. 


1-8 


50 


3,500 



/. Tests on completed lengths 601 to 7,000 Volt. 



Max. Operating Voltage. 
1,500 V. Type Letters R. S - 
Thick 



Size. 

B. & S. Gage 
14-8 

7-2 
1 -0000 

C. M. 

225,000-500,000 
525,000-1,000,000 
Over 1,000,000 



Ins. 

1-16 

5-64 
3-32 

7-64 
1-8 

9-64 



15. 
Ins. Res. 
Meg. 



600 
300 
200 

175 
150 
100 



Volts 
Test. 

4,000 
4,000 
4,000 

4,000 
4,000 
4,000 



FITTINGS, MATERIALS, ETC. 



301 



Max, 


Operating Voltage. 




2,500 V. 


Type Letters R. 


S.— 25. 






Thick 


Ins. Res. 


Volts 


Size. 


Ins. 


Meg. 


Test. 


B. & S. Gage 








14-8 


3S2 


700 


6,250 


7-2 


3-32 


350 


6,250 


1 -0000 


7-64 


250 


6,250 


C. M. 








225,000-500,000 


1-8 


200 


6,250 


525,000-1,000,000 


9-64 


175 


6,250 


Over 1,000,000 


10-64 


125 


6,250 


Max. 


Operating Voltage. 




3,500 V. 


Type Letters R. 


S.-35. 






Thick 


Ins. Res. 


Volts 


Size. 


Ins. 


Meg. 


Test. 


B. & S. Gage 








14-8 


4-32 


850 


8,750 


7-2 


4-32 


450 


8,750 


1 -0000 


4-32 


300 


8,75o 


C. M. 








225,000-500,000 


9-64 


225 


8,750 


525,000-1,000,000 


10-64 


200 


8,750 


Over 1,000,000; 


11-64 


150 


8,750 


Max. 


Operating Voltage. 




5,000 V. 


Type Letters R. 


s.— 50. 






Thick 


Ins. Res. 


Volts 


Size. 


Ins. 


Meg. 


Test. 


B. & S. Gage 








14-8 


6-32 


1,000 


12,500 


1-2 


6-32 


650 


12,500 


I -OOOO 


6-32 


450 


12,500 


C M. 








225,000-500,000 


6-32 


300 


12,500 


525,006-1,000,000 


6-32 


225 


12,500 


Over 1,000,000 


7'32 


175 


12,500 



302 MODERN ELECTRICAL CONSTRUCTION. 



Max. 


Operating Voltage. 




7,000 V. 


Type Letters R. 


S.— 70. 






Thick 


Ins. Res. 


Volts 


Size. 


• Ins. 


Meg. 


Test. 


B. & S. Gage 








14-8 


8-32 


1,200 


17,500 


7-2 


8-32 


800 


i7,5oo 


1 -0000 


8-32 


550 


17,500 


C M. 








225,000-500-000 


8-32 


400 


17,500 


525,000-1,000,000 


8-32 


275 


17,500 


Over 1,000,000 


9-32 


200 


17,500 



g. All physical tests to be made at a temperature between 
60 degrees and 90 degrees Fahrenheit. All test samples to be 
kept at a temperature within this range for at least 2 hours 
before the tests are made. 

1. The rubber compound or other approved insulation 
must be sufficiently elastic to comply with a test made as fol- 
lows : — 

A sample of wire about 20 inches long shall have the braid 
and insulation removed for about 2 inches at each end, leav- 
ing the braid and insulation on balance of sample. One end of 
the bare copper should be fastened to a clamp on a shaft of 
the diameter given below, and a weight as given below at- 
tached to the other end of the bare copper wire. The shaft 
shall then be revolved ten times in ten seconds, wrapping the 
sample in a close wind around the shaft. With the tension 
left on the sample, it should then be immersed in water for 24 
hours, immediately after which it should, while still immersed, 
be subjected to 1,500 volts alternating current for 1 minute. 







B. & S. 


Mils. 


Lbs. 


Diam. 


of shaft 


No. 14 wire 


170 


weight 10 


Diam. 


of shaft 


12 wire 


190 


weight 10 


Diam. 


of shaft 


10 wire 


275 


weight 12 


Diam. 


of shaft 


8 wire 


375 


weight 15 



2. Any rubber compound used as insulation shall be tested 
for permanent set, elongation and tensile strength as fol- 
lows : — 



FITTINGS, MATERIALS, ETC. 303 

New wire. — A test piece taken from the wire, having in- 
sulation less than five sixty-fourths inch thick, shall have 
marks placed 2 inches apart, and shall be stretched longi- 
tudinally at the rate of 12 inches per minute till the marks 
are 5 inches apart, and then be immediately released and a 
measurement taken 30 seconds thereafter, when the distance 
between the marks must not exceed 2.5 inches. The test 
piece shall then be stretched until the marks are 6 inches 
apart before rupture. The tensile strength shall not be less 
than 400 lbs. per square inch, calculated upon the original 
cross section of the test piece before stretching. 

Test pieces from wire having insulation five sixty-fourths 
inch thick or over shall be tested in a similar manner, but 
shall be stretched to 4 inches instead of 5 inches, and must 
not break until stretched 5 inches, and shall have a tensile 
strength of 400 lbs. per square inch. 

Wire tested at any time up to one year from date of man- 
ufacture. — A test piece taken from wire having insulation less 
than five sixty-fourths inch thick shall have marks placed 2 
inches apart, and shall be stretched longitudinally at the rate 
of 12 inches per minute till the marks are 4 inches apart, and 
then be immediately released and a measurement taken 30. 
seconds thereafter, when the distance between the marks must 
not exceed 2.5 inches. 

Test pieces from wire having insulation five sixty-fourths 
inch or over shall be stretched to SV2 inches instead of 4 
inches. 

h. All of the above insulations must be protected by a 
substantial braided covering, properly saturated with a pre- 
servative compound. This covering must be sufficiently strong 
to withstand all the abrasions likely to be met with in prac- 
tice, and must substantially conform to approved samples sub- 
mitted by the , manufacturer. 

i. Five chemical tests shall be made of the rubber com- 
pound as follows : Acetone extract, alcoholic potash extract, 
chloroform extract, ash and total sulphur. 

The sum total of the results of these five tests shall not 
exceed 80 per cent by weight of the total compound. 

The ash test shall be supplemented by tests to determine 
the quantity of substances other than vulcanized rubber, which 
ajre combustible, but not soluble in acetone, alcoholic potash, 



304 MODERN ELECTRICAL CONSTRUCTION. 

or chloroform, and any such substance shall be counted as 
ash. 

Tests to be made according to Underwriters' Laboratories 
specifications. 

Lead Covered Wires and Cables for Interior Work Only. 

(Type letters R. S. L.) 

;. The thickness of insulating wall of lead sheath rubber 
insulated conductors 0-600 volts to be the same as for braided 
cables, all cables to be covered with a compound filled tape 
or braid over the insulating wall. If braid is used, it shall 
be of such a thickness as to increase the required diameter 
over the insulating wall by at least one thirty-second of an 
inch, and must comply with the requirements for braid on 
braided conductors. 

If tape is used it must not be less than one sixty-fourth 
of an inch thick and must lap at least one-fourth of its width. 
The width of the tape used should not exceed twice the square 
root of the diameter of the conductor over the insulating 
wall; i. e. y 500,000 C. M. three thirty-seconds rubber, tape not 
to exceed 2 inches in width; No. 14, three sixty-fourths rub- 
ber, tape should not exceed .8 inches in width. 

The lead on single conductor cables, 0-600 volt class, sizes 
2 B. & S. and smaller, both solid and stranded, ta be not less 
than the thickness of rubber called for by Section e. On 
larger sizes the thickness of lead to be not less than the 
thickness of insulating wall called for, less one sixty-fourth 
of an inch ; i. e., thickness of lead on No. 2, one-sixteenth 
inch ; on 1,000,000 C. M., three thirty-seconds inch. On mul- 
tiple conductor cables, thickness of lead to be that called for 
by single conductor, having same diameter* over the insula- 
tion as the multiple conductor cable has over the bunched in- 
sulated conductors. 

Rubber insulated and lead sheathed cables, 601 to 7,000 
volt classes inclusive (Type letters R. S. L — 15, R. S. L — 25, 
etc.) shall comply with Section f, and the lead sheath shall 
be the same as called for in 0-600 volt class, having same di- 
ameter under the lead as 601-7,000 volt conductor. 

(Electrical test on finished leaded cables the same as on 
braided.) 

It will be noted that the specifications governing the con- 
struction and testing of rubber covered wire have been 



FITTINGS, MATERIALS, ETC. 305 

greatly amplified and made much more rigid. The previous 
specifications allowed a wire of rather poor insulating qual- 
ity and the statement has been made that "rubber covered 
wire," the insulating covering of which was entirely devoid 
of rubber, has been made to stand the tests. 

The present specifications have been drawn up in such a 
manner as to demand a very good insulating covering for the 
wire, requiring a rubber compound with about 20% of rubber. 

In the stretch test a ready method of roughly testing the 
wire in the field has been provided. To make this test remove 
the braid carefully and strip the entire rubber insulating cov- 
ering from the wire. Place two marks two inches apart and 
test the wire by stretching it as directed. "New" wire is 
wire not over thirty days old and should stretch to five inches 
and back to two and one-half inches. Wire over thirty days 
old shall be stretched to 4 inches and should then return to 
two and one-half inches. 

51. Slow-burning Weatherproof Wire. (Type Letters 
S. B. W.) 

(See Figure 165.) 

(For installation rules see No. 26 h.) 

This wire is not as burnable as ''weatherproof" nor as subject 
to softening under heat. It is not suitable for outside work. 

a. The insulation must consist of two coatings, one to be 
fireproof in character and the other to be weatherproof. The 



Figure 165. 

fireproof coating must be on the outside and must comprise 
about six-tenths of the total thickness of the wall. The com- 
pleted covering must be of a thickness not less than that 
given in the following table : — 



306 MODERN ELECTRICAL CONSTRUCTION. 

B. & S. Gage. Thickness. 

14 to 8 3-64 inch. 

7 to 2 '. 1-16 inch. 

1 to 0000 5-64 inch. 

Circular Mils. 

250,000 to 500,000 3-32 inch. 

500,000 to 1,000,000 7-64 inch. 

Over 1,000,000 1-8 inch. 

Measurements of insulating wall are to he made at the thinnest 
portion. 

b. The fireproof coating shall be of the same kind as that 
required for "slow-burning wire," and must be finished with 
a hard, smooth surface. 

c. The weatherproof coating shall consist of a stout braid, 
applied and treated as required for "weatherproof wire." 

52. Slow-burning Wire. (Type Letters S. B.) 

(For installation rules see No. 26 h.) 

a. The insulation must consist of three braids of cotton 
or other thread, all the interstices of which must be filled 
with the fireproofing compound or with material having equiv- 
alent resisting and insulating properties. The outer braid 
must be specially designed to withstand abrasion, and its sur- 
face must be finished smooth and hard. The completed cover- 
ing must be of a thickness not less than that given in the table 
under No. 51 a. 

The solid constituent of the fireproofing compound must not be 
susceptible to moisture, and must not burn even when ground in 
an oxidizable oil, making a compound which, while proof against 
fire and moisture, at the same time has considerable elasticity, and 
which . when dry will suffer no change at a temperature of 250 
degrees Fahrenheit (121 degrees Centigrade), and which will not 
burn at even a higher temperature. 

This is practically the old so-called "underwriters" insulation. It 
is especially useful in hot, dry places where ordinary insulations 
would perish, and where wires are bunched, as on the back of a 
large switchboard or in a wire tower, so that the accumulation 
of rubber insulation would .result in an objectionably large mass 
of highly inflammable material. 

53. Weatherproof Wire. (Type Letters W. R.) 

(See Figure 166.) 
(For rules for installation see No. 26 i and j.) 
a. The insulating covering shall consist of at least three 
braids, all of which must be thoroughly saturated with a dense 



FITTINGS, MATERIALS, ETC. 2>°7 

moisture-proof compound, applied in such a manner as to 
drive any atmospheric moisture from the cotton braiding, 
thereby securing a covering to a great degree waterproof and 
of high insulating power. This compound must not drip at 
160 degrees Fahrenheit (71 degrees Centigrade). The thick- 
ness of insulation must not be less than that given in the table 
under No. 51 a, and the outer surface must be thoroughly 
slicked down. 

This wire is for use outdoors, where moisture is certain and 
where fireproof qualities are not necessary. 

54. Flexible Cord. 

(For installation rules, see No. 32.) 
Cords for pendant lamps and for portable use including 
Elevator, Lighting and Control Cables, and Theatre Stage and 
Border Cable (for Cords for Portable Heating Apparatus, see 
No. 54 d.) 

a. Must be made of copper conductors, each built up from 
wires not larger than No. 26, or smaller than No. 36 B. & S. 
gage. Each conductor must have a carrying capacity not less 
than that of a No. 18 B. & S. gage wire, and must be covered 



Figure 166. 

by an approved insulation and protected from mechanical in- 
jury according to the following specifications for the several 
types of cord or cable. Each conductor must be covered with 
a tight close wind of fine cotton, or some other approved 
method must be employed to prevent a broken strand punc- 
turing the insulation and to keep the rubber compound from 
corroding the copper, and must comply with No. 49. 

b. The insulating covering on each conductor must be of 
a rubber compound, and must comply with No. 50 c, g and *, 
and must have a thickness of wall not less than that given in 
the following table : — * 

Thickness, inches. 
B. & S. Gage. Dry Places. Damp Places. 

18 and 16 1-32 3-64 

14 3-64 3-64 

For exception see c, 2. 



308 MODERN ELECTRICAL CONSTRUCTION. 

Every completed single conductor shall be tested by passing 
it through a spring metal spiral not less than 6 inches long, so 
formed as to come in contact with all points on the circum- 
ference of the wire, while a voltage of not less than 500 volts 
for one sixty-fourth inch insulation, not less than 1,000 volts 
for one thirty-second inch insulation or not less than 1,500 
volts for three sixty-fourths inch insulation is applied to the 
conductor and to the spiral. 

The completed cord shall be subjected to a 1 minute test 
between conductors of 1,000 volts for one sixty-fourth inch 
insulation, 2,000 volts for one thirty-second inch insulation 
and 2,500 volts for three sixty-fourths inch insulation. 

The insulating coverings in the above tests shall be suf- 
ficient to resist puncture or breakdown. The source of electro- 
motive force shall be the same as that specified in No. 50 c. 

c. Must have on outer protecting covering as follows : — 

1. For Pendant Lamps. — (Type Letter C.) (See Figure 
167.) In this class is to be included all flexible cord, which, 
under usual conditions, hangs freely in air, and which is not 
likely to be moved sufficiently to come in contact with sur- 
rounding objects. 

It should be noted that pendant lamps provided with long 
cords, so that they can be carried about or hung over nails, 
or on machinery, etc., are not included in this class, even 
though they are usually allowed to hang freely in air. 

Each conductor must have an approved braided covering 
so put on and sealed in place that when cut it will not fray 
out. 

For use in damp places (Type Letters C. Wp.) the in- 
sulation must be at least three sixty-fourths of an inch thick 




Figure 167. 

and the braided coverings must either be thoroughly saturated 
with a moisture proof preservative compound or be enclosed 
in an outer braided moisture-proof preservative covering over 
the whole. 



FITTINGS, MATERIALS, ETC. 



309 



It will be specially noted that the thickness of rubber on 
cords for use in damp places must be not less than 3/64th of 
an inch. The object is to obtain a substantial thickness of 
rubber between wires of opposite polarity. "Portable" cord, 
"packing houses" cord, "brewery" cords and other cords of 
similar construction having only a i/32d inch rubber insula- 
tion must not be used in damp places. 

2. For Portables. — (Type Letter P.) (See Figure 168.) 
Flexible cord for portable use except in offices, dwellings or 




Figure 168. 

similar places, where cord is not liable to rough usage and 
where appearance is an essential feature, must meet all the re- 
quirements for flexible cord for pendants and in addition must 
have a tough, braided cover over the whole. There must also 
be an extra layer of rubber between the outer cover and the 
flexible cord. 

For use in damp places (Type Letters P. Wp.) the insula- 
tion must be at least three sixtv-fourths of an inch thick and 




Figure 169. 



the cord must have its outer covering saturated with a moist- 
ure-proof preservative compound thoroughly slicked down or 
must have a filler of approved material instead of the extra 
layer of rubber and have two outer braids saturated with a 
moisture-proof compound with the exterior surface thor- 
oughly slicked down. 

In offices, dwellings, or in similar places (Type Letters 
P. O.) (see Figure 169), where cord is not liable to rough 
usage and where appearance is an essential feature, flexible 



310 MODERN ELECTRICAL CONSTRUCTION. 

cord for portable use must meet all of the requirements for 
flexible cord for "pendant lamps,'' both as to construction 
and thickness of insulation, and in addition must have a tough, 
braided cover over the whole, or providing there is an extra 
layer or rubber between the flexible cord and the outer cover, 
the insulation proper on each stranded conductor of cord may 
be of one sixty-fourth of an inch in thickness instead of as re- 
quired for pendant cords. 

Fexible cord for portable use may, instead of the outer 
coverings described above, have an approved metal, flexible 
armor. (Type Letters P. A.). 

d. For Portable Heating Apparatus. — (Type Letter H.) 
(See Figure 170.) Applies to all smoothing and sad irons and 
to any other heating device requiring over 250 watts. Must 
be made up as follows: — 

1. Conductors must comply with Section a, or may be of 
braided copper. If braided, each wire to be not larger than 
No. 30, or smaller than No. 36 B. & S. gage, except for con- 




Figure 170. 

ductors having a greater carrying capacity than No. 12 B. & 
S. gage when each wire may be as large as No. 28 B. & S. 
gage. 

2. An insulating covering of rubber or other approved 
material not less than one sixty-fourth inch in thickness. 

3. A braided covering not less than one thirty-second 
inch thick composed of long fibre absestos and having not over 
10 per cent of carbon by weight. 

4. An outer reinforcing covering not less than one sixty- 
fourth inch thick, especially designed to resist abrasion, must 
enclose either all the conductors as a whole or each conductor 
separately. 

5. The completed cord shall be subjected to a 1 minute 
test between conductors of 1,500 volts, and must resist punc- 
ture or breakdown when so tested. The source of electro- 
motive force to be the same as that specified in No. 50. 

e. Theatre Stage Cable. — (Type Letter T.) (See Figure 
171.) Shall consist of not more than three flexible cooper con- 



FITTINGS, MATERIALS, ETC. 311 

ductors, each of a capacity not exceeding No. 4 *B. & S. gage, 
each of which shall be built up of wires not larger than No. 
26 B. & S. gage. Each conductor to have a tight close wind 
of cotton, or some other approved method must be employed 
to prevent a broken strand puncturing the insulation and to 
keep the rubber compound from corroding the copper. The 
insulation proper to be of rubber complying with No. 50 b and 
d and with requirements of No. 50 c, except that insulations 
less than three sixty-fourths of an inch in thickness (con- 
ductors having a capacity less than No. 14 B. & S. gage wire) 
must show an insulation resistance of not less than 50 
megohms per mile during two weeks' immersion in water at 
70 degrees Fahrenheit (21 degrees Centigrade), must have on 
each conductor an outer protective braided covering properly 
saturated with a preservative compound. The conductors to 
be twisted together, a filler of approved material being used 




Figure 171. 

to make cable round and to act as a cushion, and finished with 
two weatherproof braids over the whole. 

The completed cable must be of such a flexible nature as 
to be readily handled, and when laid on the floor must align 
itself to the floor level. 

/. Border Cables. — (Type Letter B.) (See Figure 172.) 
Shall consist of flexible copper conductors, each of which shall 
be built up of wires not larger than No. 26 B. & S. gage. 
Each conductor to have a tight close wind of cotton, or some 
other approved method must be employed to prevent a broken 
strand puncturing the insulation, and to keep the rubber com- 
pound from corroding the copper. The insulation proper to 
be of rubber complying with requirements of No. 50 b, c and 
d, must have on each conductor an outer protective braided 
covering properly saturated with a preservative compound. 
The conductors to be cabled together and finished with two 
weatherproof braids over the whole. 

g. Elevator Lighting and Control Cables. — (Type Letter 
E.) Must comply with the requirements for threatre cable as 



312 MODERN ELECTRICAL CONSTRUCTION. 

regards insulation proper and the construction and covering 
of the individual conductors, except that none of these con- 
ductors shall be smaller than No. 14 B. & S. gage for elevator 
lighting cables, or No. 16 for elevator control cables. The 
outer covering shall consist either of three braids or of an 
extra layer of rubber and one or more outer braids. All 
braids must be properly treated with a preservative compound. 

55. Fixture Wire. 

(See Figure 173.) 

(For installation rules, see Nos. 24 e, and 26 v to y. For 

construction of fixtures, see No. 77,) 

a. Fixtures may be wired with approved flexible cord 
(see No. 54 a to c) or with approved rubber covered wire 
No. 14 B. & S. gage or larger (see No. 50). 

In wiring certain designs of show-case fixtures, ceiling 
bulls-eyes and similar appliances in which the wiring is ex- 




Figure 172. 



posed to temperatures in excess of 120 degrees Fahrenheit 
(49 degrees Centigrade), from the heat of the lamps, slow- 
burning wire may be used (see No. 52). All such forms of 
fixtures must be submitted for examination, test and approval 
before being introduced for use. 

For other wires for use in fixtures the following rules apply. 
(Type letters F-64 and F-32.) 
b. May be made of solid or stranded conductors, with no 
strands smaller than No. 30 B. & S. gage, and must have a 



FITTINGS, MATERIALS, ETC. 313 

carrying capacity not less than that of a No. 18 B. & S. gage 
wire. 

c. Solid conductors must be thoroughly tinned. If a 
stranded conductor is used, it must be covered by a tight, close 
wind of fine cotton, or some other approved method must be 
employed to prevent a broken strand puncturing the insula- 
tion and to keep the rubber compound from corroding the cop- 
per and must comply with the requirements of No. 49. 

Figure 173. 

d. The insulation on each conductor must consist of a 
rubber compound homogeneous in character, adhering to the 
conductor or to the separator, if one is used, and not less 
than one sixty-fourth inch in thickness for No. 18 B. & S. 
gage wire and not less than one thirty-second inch for No. 
16 B. & S. gage. 

e. Must be protected with a covering or braid at least 
one sixty-fourth inch in thickness, sufficiently tenacious to 
withstand the abrasion of being pulled into the fixture, and 
sufficiently elastic to permit the wire to be bent around a cyl- 
inder with twice the diameter of the wire without injury to 
the braid. 

/. Must successfully withstand the tests specified in Nos. 
50 c, g and i. 

Sufficient data is not available for publication of values similar 
to those in No. 49 d and e, for voltage and resistance tests of in- 
sulations one sixty-fourth and one thirty-second inch thick, com- 
posed of rubber compounds required by present specifications on 
wires and suited for use in fixture wiring. 

56. Conduit Wire. (Type Letters R. D.) 

(For installation rules, see No. 26 n to p.) 

a. Single wire for lined conduits must comply with the re- 
quirements of No. 50. (See Figure 174.) For unlined con- 
duits it must comply with the same requirements (except that 
tape may be substituted for braid), and in addition there must 
be a second outer fibrous covering, at least one thirty-second 



314 



MODERN ELECTRICAL CONSTRUCTION. 



of an inch in thickness for wires larger than No. 10 B. & S. 
gage, and at least one sixty-fourth of an inch in thickness for 
wires No. 10 B. & S. gage or less in size; this fibrous cov- 
ering to be sufficiently tenacious to withstand abrasion of 
being hauled through the metal conduit. (Figures 175 and 

b. For twin or duplex wires in lined conduit, each con- 
ductor must comply with the requirements of No. 50 (except 
that tape may be substituted for braid on the separate con- 
ductors), and must have a substantial braid covering the 



Figure 174. 



Figure 175. 






Figure 176. 



whole. For unlined conduit each conductor must comply 
with requirements of No. 50 (except that tape may be sub- 
stituted for braid), and in addition must have a braid covering 
the whole, at least one thirty-second of an inch in thickness 
and sufficiently tenacious to withstand the abrasion of being 
hauled through the metal conduit. (Figure 177.) 

c. For concentric wire, the inner conductor must comply 
with the requirements of No. 50 (except that tape may be 
substituted for braid), and there must be outside of the outer 
conductor the same insulation as on the inner, the whole to 
be covered with a substantial braid, which for unlined con- 
duits must be at least one thirty-second of an inch in thick- 





Figure 177. 



Figure 178. 



ness, and sufficiently tenacious to withstand the abrasion of 
being hauled through the metal conduit. (Figure 178.) 

d. The braids or tapes called for in sections a, b and c, 
must be properly saturated with a preservative compound. 

The braid or tape required around each conductor in duplex, twin 
and concentric cables is to hold the rubber insulation in place and 
prevent jamming and flattening:. 



FITTINGS, MATERIALS, ETC. 315 

57. Armored Cable. (Type Letters A. C.) 

(See Figure 179.) 

(For installation rules, see No. 27.) 

a. The material, weight and form of armor must be such 
as to afford under conditions likely to be met in practice, pro- 




Figure 179. 

tection substantially equivalent in all respects to that afforded 
by unlined rigid conduit. 

b. The conductors in same, single, or multiple, must have 
an insulating covering as required by No. 50. The whole 
bunch of conductors and fillers, if any, must have a separate 
exterior covering, and the filler, if any is used to secure a 
round exterior, must be impregnated with a moisture repellant. 
58. Interior Conduits. 

(For installation rules, see Nos. 26 n to p and 27.) 

a. Each length of conduit, whether lined or unlined, 
must have the maker's name or initials stamped in the 
metal or attached thereto in a satisfactory manner, so that 
inspectors can readily see the same. 

The use of paper stickers or tags cannot be considered satisfac- 
* tory methods of marking, as they are readily loosened and lost off 
in the ordinary handling of the conduit. 

Metal Conduits with Lining of Insulating Material. 

(See Figure 180.) 

b. The metal covering or pipe must be at least as strong 
as that specified in 58;'. 

c. Must not be seriously affected externally by burning 



3l6 MODERN ELECTRICAL CONSTRUCTION. 

out a wire inside the tube when the iron pipe is connected to 
one side of the circuit. 

d. Must have the insulating lining firmly secured to the 
pipe. 

e. The insulating lining must not crack or break when a 
length of the conduit is uniformly bent at temperature of 212 
degrees Fahrenheit (100 degree Centigrade), to an angle of 
90 degrees, with a curve having a radius of fifteen inches, for 
pipes of one inch and less, and fifteen times the diameter of 
pipe for larger sizes. 

f. The insulating lining must not soften injuriously at 
any temperature below 212 degrees Fahrenheit (100 degrees 




Figure 180. 

Centigrade) and must leave water in which it is boiled prac- 
tically neutral. 

g. The insulating lining must be at least one thirty-sec- 
ond of an inch in thickness. The materials of which it is 
composed must be of such a nature as will not have a de- 
teriorating effect on the insulation of the conductor, and be 
sufficiently tough and tenacious to withstand the abrasion 
test of drawing long lengths of conductors in and out of 
same. 

h. The insulating lining must not be mechanically weak 
after three days' submersion in water, and must not absorb 
more than ten per cent of its weight of water during 100 hours 
of submersion. 

i. All elbows or bends must be so made that the conduit 
or lining of same will not be injured. The radius of the 
curve of the inner edge of any elbow must not be less than 
three and one-half inches. 
Unlined Metal Conduits. 

(See Figure 181.) 
Rigid: — 

;. Finished conduit to have weight per hundred feet not 
less than that given in the following table : — 



FITTINGS, MATERIALS, ETC. 317 

Trade size Approx. Internal Min. Thick- Wt. per 100 ft. 
Inches. Diameter ness of wall Pounds 

Inches. Inches. 

V2 .62 .100 75 

Yi .82 .105 104 

1 1.04 .125 152 

iVa 1.38 .135 209 

lY 2 1.61 .140 250 

2 2.06 .150 350 

2.y 2 2.46 .200 535 

3 3.06 .210 710 

k. Pipe should be of sufficiently true circular section to 
admit of cutting true, clean threads, and should be very closely 




Figure 181. 

the same in wall thickness at all points with clean square 
weld. 

/. The pipe from which the conduit is made must be thor- 
oughly cleaned to remove all scale and must then be protected 
against effects of oxidation, by baked enamel, zinc or other 
approved coating which will not soften at ordinary temper- 
atures, and of sufficient weight and toughness to success- 
fully withstand rough usage likely to be received during ship- 
ment and installation ; and of sufficient elasticity to prevent 
flaking when one-half inch conduit is bent in a curve the inner 
edge of which has radius of 3^2 inches. All conduit must have 
an interior coating of a character and appearance which will 
readily distinguish it from ordinary commercial pipe com- 
monly used for other than electrical purposes. 

_ m. All elbows or bends must be so made that the conduit 
will not be injured. The radius of the curve of the inner 
edge of any elbcw not to be less than three and one-half 
inches. 
Flexible: — 

n. The material, weight and form of flexible metal con- 



318 MODERN ELECTRICAL CONSTRUCTION. 

duits must be such as to afford under conditions likely to be 
met in practice, protection substantially equivalent in all 
respects to that afforded by rigid unlined metal conduits. 

59. Outlet, Junction and Flush Switch Boxes. 

(See Figure 182.) 

(For installation rules see Nos. 27 and 28. For boxes for 
panel-boards, cut-outs and switches other than Hush 
switches see No. 70.) 

a. Must be of pressed steel having wall thickness not less 
than .078 inch (No. 14 U. S. metal gage), or of cast metal 
having wall thickness not less than one-eighth inch. Junc- 
tion boxes of larger sizes must comply with requirements of 
No. 70, but must in all cases be of metal. 

b. Must be well galvanized, enameled or otherwise prop- 
erly coated, inside and out, to prevent oxidation. 

It is recommended that the protective coating be of conductive 
material such as tin or zinc. 

c. Must be so made that all openings not in use will be 
effectively closed by metal which will afford protection sub- 
stantially equivalent to the walls of the box. 

Fittings which are designed for bringing conductors from 
metal conduits to exposed wiring must be provided with non- 
absorptive, non-combustible, insulating bushings, which, ex- 
cept with flexible cord, must separately insulate each con- 
ductor. 

d. Must be plainly marked, where it may readily be 
seen when installed, with the name or trademark of the manu- 
facturer. 

e. Must, in case of combination gas and electric outlets, 
be so arranged that connection with gas pipe at outlet may 
be made by means of an approved device. 

Must be arranged to secure in position the conduit or flex- 
ible tubing protecting the wire. 

This rule will be complied with if the conduit or tubing is firmly 
secured in position by means of some approved device which may 
or may not be a part of the box. 

f. Boxes used with lined conduit must comply with the 
foregoing requirements, and in addition must have a tough 



FITTINGS, MATERIAIS, ETC. 



319 



and tenacious insulating lining at least one thirty-second inch 
thick, firmly secured in position. 

g. Switch and outlet boxes must be so arranged that 
they can be securely fastened in place independently of the 
support afforded by the conduit piping, except that when en- 
tirely exposed, approved boxes, which are threaded so as to be 
firmly supported by screwing on to the conduit pipe, may be 
used. 




Figure 182. 

h. Switch boxes must completely enclose the switch on 
sides and back, and must provide a thoroughly substantial 
support for it. The retaining screws for the box must not be 
used to secure the switch in position. 

i. Covers for outlet boxes if made of metal must be 
equal in thickness to that specified for the walls of the box, 
or must be of metal lined with an insulating material not less 
than one thirty-second inch in thickness, firmly and perma- 
nently secured to the metal. Covers may also be made of 
porcelain or other approved material, provided they are of 
such form and thickness as to afford suitable protection and 
strength. 

60. Mouldings. 

(For installation rules see Nos. 26 k to m.) 
Wooden Mouldings. 

a. Must have, both outside and inside, at least two coats 
of waterproof material, or be impregnated with a moisture 
repellent. 



320 MODERN ELECTRICAL CONSTRUCTION. 

b. Must be made in two pieces, a backing and a capping, 
and must afford suitable protection from abrasion. Must 
be so constructed as to thoroughly encase the wire, be pro- 
vided with a tongue not less than one-half inch in thickness 
between the conductors, and have exterior walls which un- 
der grooves shall not be less than three-eighths inch in thick- 
ness, and on the sides not less than one-fourth inch in thick- 
ness. 

It is suggested that only hard wood be used. 

Metal Mouldings. 

(See Figure 183.) 

(For installation rules see Nos. 26 k to m and 29.) 

c. Each 1-ength of such moulding must have maker's name 
or trade-mark stamped in the metal, or in some manner per- 
manently attached thereto, in order that it may be readily 
identified in the field. 

The use of paper stickers or tags cannot be considered satisfac- 
tory methods of marking, as they are readily loosened and lost off 
in ordinary handling of the moulding. 

d. Must be constructed of iron or steel with backing at 
least .050 inch in thickness, and with capping not less than 




Figure 183. 

.040 inch in thickness, and so constructed that when in place 
the raceway will be entirely closed ; must be thoroughly gal- 
vanized or coated with an approved rust preventive both in- 
side and out to prevent oxidation. 

e. Elbows, couplings and all other similar fittings must be 
constructed of at least the same thickness and quality of metal 
as the moulding itself, and so designed that they will both 
electrically and mechanically secure the different sections to- 
gether and maintain the continuity of the raceway. The in- 



FITTINGS, MATERIALS, ETC. 321 

terior surfaces must be free from burrs or sharp corners which 
might cause abrasion of the wire coverings. 

f. Must at all outlets be so arranged that the conductors 
cannot come in contact with the edges of the metal, either of 
capping or backing. Specially designed fittings which will in- 
terpose substantial barriers between conductors and the edges 
of metal are recommended. 

g. When backing is secured in position by screws or bolts 
from the inside of the raceway, depressions must be pro- 
vided to render the heads of the fastenings flush with the 
moulding. 

h. Metal mouldings must be used for exposed work only 
and must be so constructed as to form an open raceway to 
be closed by the capping or cover after the wires are laid in. 

61. Tubes and Bushings. 

a. Construction. 

(See Figure 184.) 

Must be made straight and free from checks or rough 
projections, with ends smooth and rounded to facilitate the 
drawing in of the wire and prevent abrasion of its covering. 

b. Material and Test. 

Must be made of non-combustible, insulating material, 
which, when broken and submerged for 100 hours in pure 




Figure 184. 

water at 70 degrees Fahrenheit (21 degrees Centigrade), will 
not absorb over one-half of one per cent of its weight. 

c. Marking. 

Must have the name, initials or trade-mark of the manu- 
facturer stamped in the ware. 



$22 MODERN ELECTRICAL CONSTRUCTION. 

d. Sizes. 

Dimensions of wall and heads must be at least as great 
as those given in the following table: — 



Diameter 


External 


Thick- 


External 


Length 


of 


Diameter. 


ness of 


Diameter 


of 


Hole. 




Wall. 


of Head. 


Head. 


ft in. 


ft in. 


% in. 


it in. 


% in. 


% 


tt 


ft 


11 


3 /2 


y 3 


41 


ft 


1ft 


% 


% 


if 


ft 


1ft 


% 


% 


1ft 


ft 


Hi 


5 /s 


i 


1ft 


& 


lit 


% 


1% 


lit 





2ft 


% 


iy 8 


2ft 


Ji 


21i 


% 


i% 


2ft 


41 


3ft 


% 


2 


211 


15 
3 2 


3ft 


% 


2*/ 4 


3ft 


11 


311 


1 


2% 


° 16 


ii 


4ft 


1 



An allowance of one sixty-fourth of an Inch for variation In 
manufacturing will be permitted, except in the thickness of the 
wall. 

62. Cleats. 

a. Construction. 

(See Figure 185.) 

Must hold the wire firmly in place without injury to its 
covering. 

Sharp edges which may cut the wire should be avoided. 

b. Supports. 

Bearing points on the surface must be made by ridges or 
rings about the holes for supporting screws, in order to avoid 
cracking and breaking when screwed tight. 

c. Material and Test. 

Must be made of non-combustible, insulating material, 
which, when broken and submerged for 100 hours in pure 
water at 70 degrees Fahrenheit (21 degrees Centigrade), will 
not absorb over one-half of one per cent of its weight. 



FITTINGS, MATERIALS, ETC. $ 2 3 

d. Marking. 

Must have the name, initials or trade-mark of the manu- 
facturer stamped in the ware. 

e. Sizes. 

Must conform to the spacings given in the following 
table :— 

Distance from Wire Distance between 

Voltage. to Surface. Wires. 

0-300 y 2 inch 2V 2 inches 

This rule will not be interpreted to forbid the placing of the 
neutral of a three-wire system in the center of a three-wire cleat 
where the difference of potential between the outside wires is not 
over 300 volts, provided the outside wires are separated two and 
one-half inches. 

63. Flexible Tubing. 

(See Figure 186.) 
(For installation rules see No. 26 e. s and u.) 

a. Must have a sufficiently smooth interior surface to al- 
low the ready introduction of the wire. 




Figure 185. 

b. Must be constructed of or treated with materials which 
will serve as moisture repellents. 

c. The tube must be so designed that it will withstand 
all the abrasion likely to be met with in practice. 

d. The linings, if any, must not be removable in lengths 
of over three feet. 

< e. The one-fourth inch tube must be so flexible that it 
will not crack or break when bent in a circle with six-inch 
radius at 50 degrees Fahrenheit (10 degrees Centigrade, and 



324 MODERN ELECTRICAL CONSTRUCTION. 

the covering must be thoroughly saturated with a dense moist- 
ureproof compound which will not slide at 150 degrees Fahren- 
heit (65 degrees Centigrade). Other sizes must be as well 
made. 

/. Must not convey fire on the application of a flame from 
Bunsen burner to the exterior of the tube when held in a 
vertical position. 

g. Must be sufficiently tough and tenacious to withstand 
severe tension without injury; the interior diameter must not 




Figure 186. 

be diminished or the tube opened up at any point by the 
application of a reasonable stretching force. 

h. Must not close to prevent the insertion of the wire 
after the tube has been kinked or flattened and straightened 
out. 

i. Must have a distinctive marking the entire length of 
the tube, so that tubing may be readily identified in the field. 

64. Knobs. 

a. Construction. 

Split knobs must be constructed in two parts, a base and 
a cap, arranged to hold the wire firmly in place without in- 
jury to its covering. Sharp edges must be avoided. Solid 
knobs must be constructed with smooth groove, to contain 
wire. 

b. Supports. 

Bearing points on the surface wired over must be made 
by a ring or by ridges on the outside edge of the base, to 
provide for stability. At least one-fourth inch surface separa- 
tion must be maintained between the supporting screw or nail 
and the conductor, and the knob must be so constructed that 
the supporting screw or nail cannot come in contact with the 
conductor. For wires larger than No. 4 B. & S. gage, split 
knobs (or single wire cleats) must be so constructed as to 
require the use of two supporting screws. 



FITTINGS, MATERIALS, ETC. 



325 



c. Material and Test. 

Must be made of non-combustible, insulating material, 
which, when broken, and submerged for one hundred hours 
in pure water at 70 degrees Fahrenheit (21 degrees Centi- 
grade) will not absorb one-half of one per cent of its weight. 

d. Marking. 

Must have the name, initials or trade-mark of the man- 
ufacturer stamped in the ware. 

e. Sizes. 

Must be so constructed as to separate the wire at least one 
inch from the surface wired over, and also conform to the 
following" minimum dimensions : — 





Size of 
Base, Inches. 


Solid Knobs, 
Groove, 
Inches. 


> 



So 

•- © 

°.d 


Size 

of 

Wire 


OB 

,Q 

O 

d 
Mm 

u & 

«% 

uQ 


Square Knobs 

or Single 

Wire Cleats. 




03 

So 


Inclusive. 


p 


$-. 
<D 
+J 
0) 

B 

od 

s 


HH 




-a 


a 


bo a 

O U 


14-1 

8-4 

2-00 

000-300,000 1 
CM. f 

400,000- 1 

1,000,000 V 

C. M. 1 


1V2 

2 
2% 

3 


% 
% 

1 

. 1% 


1% 

2 

2% 
3% 


ft 
ft 
ft 

ft 

% 


y 4 
ft 

% 

154 


% 
% 
% 

% 

1 



("For installation rules see Nos. 8 c, 19 20 b and 24.) 



3 2 & MODERN ELECTRICAL CONSTRUCTION. 

General Rules. 

a. Must, when used for service switches, indicate, on in- 
spection, whether the current be "on" or "off." 

b. Must, for constant-current systems, close the main cir- 
cuit and disconnect the branch wires when turned "off;" must 
be so construced that they shall be automatic in action, not 
stopping between points when started, and must prevent an 
arc between the points under all circumstances. They must 
indicate whether the current be "on" or "off." 

Knife Switches. 

(See Figure 187.) 

Knife switches must be made to comply with the following Spe- 
cifications, except in those few cases where peculiar design allows 
the switch to fulfill the general requirements in some other way, 
and where it can successfully withstand the test of Section i. In 
such cases the switch should be submitted for special examination 
before being used. 

c. Base. 

Must be mounted on non-combustible, non-absorptive, in- 
sulating bases. Other materials than slate, marble or porcelain 
must be submitted for special examination before being used. 
Bases with an area of over twenty-five square inches must 
have at least four supporting screws. Holes for the support- 
ing screws must be so located or countersunk that there will 
be at least one-half of an inch space, measured over the sur- 
face, between the head of the screw or washer and the near- 
est live metal part, and in all cases when between parts of op- 
posite polarity must be countersunk. 

d. Mounting. 

Pieces carrying the contact jaws and hinge clips must be 
secured to the base by at least two screws, or else made with 
a square shoulder, or provided with dowel-pins, to prevent pos- 
sible turnings, and the nuts or screw-heads on the under side 
of the base must be countersunk not less than one-eighth inch 
and covered with a waterproof compound which will not melt 
below 150 degrees Fahrenheit (65 degrees Centigrade). 



FITTINGS, MATERIALS, ETC. 327 

e. Hinges. 

Hinges of knife switches must not be used to carry cur- 
rent unless they are equipped with spring washers, held by 
lock-nuts or pins, or their equivalent, so arranged that^ a firm 
and secure connection will be maintained at all positions of 
the switch blades. 

Spring washers must be of sufficient strength to take up any 
wear in the hinge and maintain a good contact at all times. 

/. Metal. 

All switches must have ample metal for stiffness and to 
prevent rise in temperature of any part of over 50 degrees 
Fahrenheit (28 degrees Centigrade), at full load, the con- 
tacts being arranged so that a thoroughly good bearing at 




Figure 187. 

every point is obtained with contact surfaces advised for pure 
copper blades of about one square inch for each seventy-five 
amperes ; the whole device must be mechanically well made 
throughout. 

g. Cross-Bars. 

All cross-bars less than three inches in length must be 
made of insulating material. Bars of three inches and over, 
which are made of metal to insure greater mechanical 
strength, must be sufficiently separated from the jaws of the 
switch to prevent arcs following from the contacts to the bar 
on the opening of the switch under any circumstances. Metal 
bars should preferably be covered with insulating material. 

To prevent possible turning or twisting the cross-bar must 



328 MODERN ELECTRICAL CONSTRUCTION. 

be secured to each blade by two screws, or the joints made 
with square shoulders or provided with dowel-pins. 

h. Connections. 

Switches for currents of over thirty amperes must be 
equipped with lugs, firmly screwed or bolted to the switch, 
and into which the conducting wires shall be soldered. For 
the smaller sized switches simple clamps can be employed, 
provided they are heavy enough to stand considerable hard 
usage. 

Where lugs are not provided, a rugged double-V groove clamp is 
advised. A set screw gives a contact at only one point, is more 
likely to become loosened, and is almost sure to cut into the wire. 
For the smaller sizes, a screw and washer connection with up- 
turned lugs on the switch terminal gives a satisfactory contact. 

i. Test. 

Must operate successfully at 50 per cent overload in am- 
peres and 25 per cent excess voltage, under the most severe 
conditions with which they are liable to meet in practice. 

This test is designed to give a reasonable margin between the 
ordinary rating of the switch and the breaking-down point, thus 
securing a switch which can always safely handle its normal load. 
Moreover, there is enough leeway so that a moderate amount of 
overloading would not injure the switch. 

j. Marking. 

Must be plainly marked where it will be visible, when the 
switch is installed, with the name of the maker and the cur- 
rent and the voltage for which the switch is designed. 

Triple pole switches designed with 125 volt spacings, between ad- 
jacent blades, should be marked 125 volts, and may be used on D. 
C. 3-wire systems having 125 volts between adjacent wires and 
250 volts between the two outside wires. 

k. Spacings. 

Spacings must be at least as great as those given in the 
following table : — 



FITTINGS, MATERIALS, ETC. 



329 



Not over 125 volts D. C. and A. C. 

For Switchboards and Panel Boards: — 





Minimum 


Minimum 




separation of 
nearest metal 


break- 
distance. 


10 amperes 
30 amperes 
60 amperes 


parts of oppo- 
site polarity. 
Yi inch 
1 inch 
l% inch 


Y 2 inch 

Y4 inch 

1 inch 



The 10-ampere switch must have ample metal for stiff- 
ness, and to prevent rise in temperature of any part of more 
than 50 degrees Fahrenheit (28 degrees Centigrade) when 
carrying 30 amperes, the contacts being arranged so that a 
thoroughly good bearing at every point is obtained with con- 
tact surface advised for pure copper blades of about 0.4 square 
inch. 

Not over 125 volts D. C. and A. C. 
For Individual Switches : — 



30 amperes 

60 and 100 amperes 
200 and 300 amperes 
400 and 600 amperes 
800 and 1,000 amperes 



iJ4 m ch 
iV 2 inch 
2*4 inch 
2^4' inch 
3 inch 



1 inch 
1^4 inch 

2 inch 
2V2 inch 
2% inch 



The 300-ampere switch must not be equipped with cut-out 
terminals. 



2 so volts only D. C. and A. C. 

For all switches. 
30 amperes 

Not over 250 volts D. C. 
nor over 500 volts A. C, 

For all switches : — 
30, 60 and 100 amperes 
200 and 300 amperes 
400 and 600 amperes 
800 and 1,000 amperes 



1^4 inch 



2J4 inch 

2*A inch 

2Y\ inch 

3 inch 



\Vi inch 



2 inch 
2J4 inch 
2y 2 inch 
2J4 inch 



The above switches must be stamped "250 V. D. C, 500 
V. A. C" 



330 MODERN ELECTRICAL CONSTRUCTION. 

The 30-ampere switch must have ample metal to prevent 
rise in temperature of any part of more than 50 degrees 
Fahrenheit (28 degrees Centigrade) when carrying 60 amperes, 
the contacts being arranged so that a thoroughly good bear- 
ing at every point is obtained with contact surfaces advised 
for pure copper blades of about 0.8 square inch. 

The 300-ampere switch must not be equipped with cut-out 
terminals. 

Cut-out terminals on switches for over 250 volts must be 
designed and spaced for 600 volt fuses, and in such cases the 
switches must be stamped "500 V. A. C." 

Not over 600 volts D. C. and A. C. 

For all switches : — 

30 and 60 amperes 4 inch 3 J A inch 

100 amperes 4^ inch 4 inch 

The 30-ampere switch must have ample metal to prevent 
rise in temperature of any part of more than 50 degrees 
Fahrenheit (28 degrees Centigrade) when carrying 60 am- 
peres, the contacts being arranged so that a thoroughly good 
bearing at every point is obtained with contact surfaces ad- 
vised for pure copper blades of about 0.8 square inch. 

Auxiliary breaks or the equivalent are recommended for 
D. C. switches designed for over 250 volts, and must be pro- 
vided on D. C. switches designed for use in breaking cur- 
rents greater than 100 amperes at a voltage of over 250. 

For three-wire direct current and three-wire single phase 
systems the separations and break distances for plain three- 
pole knife switches must not be less than those required in 
the above table for switches designed for the voltage between 
the neutral and outside wires. 

Snap Switches. 

(See Figures 188 and 189.) 

Flush, push-button, door, fixture and other snap switches used on 
constant-potential systems, must be constructed in accordance with 
the following specifications. 

/. Base. 

Current-carrying parts must be mounted on non-com- 
bustible, non-absorptive, insulating bases, such as slate or 



FITTINGS, MATERIALS, ETC. 



331 



porcelain, and the holes for supporting screws should be 
countersunk not less than one-eighth of an inch. There must 
in no case be less than three sixty-fourths of an inch space 
between supporting screws and current-carrying parts. 

Sub-bases of non-combustible, non-absorptive, insulating 
material, which will separate the wires at least one-half of 




Figure 188. 



an inch from the surface wired over, must be furnished with 
all snap switches used in exposed or moulding work. 

m. Mounting. 

Pieces carrying contact jaws must be secured to the base 
by at least two screws, or else made with a square shoulder, 
or provided with dowel-pins or otherwise arranged, to pre- 
vent possible turnings ; and the nuts or screw heads on the 
under side of the base must be countersunk not less than one- 
eighth inch, and covered with a waterproof compound which 
will not melt below 150 degrees Fahrenheit (65 degree Centi- 
grade). 



n. 



Metal. 



All switches must have ample metal for stiffness and to 
prevent rise "in temperature of any part of over 50 degrees 
Fahrenheit (28 degrees Centigrade) at full load. The whole 
device must be mechanically well made throughout. 

0. Insulating Material. 

Any material used for insulating current-carrying parts 
must retain its insulating and mechanical strength when sub- 
ject to continued use, and must not soften at a temperature 
of 212 degrees Fahrenheit (100 degrees Centigrade). 



332 



MODERN ELECTRICAL CONSTRUCTION. 



p. Binding Posts. 

Binding posts must be substantially made, and the screws 
must be of such size that the threads will not strip when set 
up tight. 

A set-screw is likely to become loosened, and is almost sure to 
cut into the wire. A binding screw under the head of which the 
wire may be clamped and a terminal plate provided with upturned 
lugs or some other equivalent arrangement, afford reliable contact. 
Switches with the set-screw form of contact will not be approved. 

q. Covers. 

Covers made of conducting material, except face plates for 
flush switches, must be lined on sides and top with insulat- 




Figure 189. 



ing, tough and tenacious material at least one thirty-second 
inch in thickness, firmly secured so that it will not fall out 
with ordinary handling. The side lining must extend slightly 
beyond the lower edge of the cover. 

r. Handle or Button. 

The handle or button or any exposed parts must not be 
in electrical connection with the circuit. 

s. Test. 

Must "make" and "break" with a quick snap, and must not 
stop when motion has once been imparted by the button or 
handle. 



FITTINGS, MATERIALS, ETC. 333 

Snap switches of the spring break pattern, normally complying 
with the above requirements, but with movement of the contact 
carrier under control of the operator at any point in the operation 
of the device, must be considered in a class with switches of the 
regular knife blade pattern and conform to the specifications of 
Section k. 

Must operate successfully at 50 per cent overload in am- 
peres and at 125 volt direct current, for all 125 volt or less 
switches, and at 250 volts direct current, for all 126 to 250 
volt switches under the most severe conditions which they 
are liable to meet in practice. For switches rated higher than 
ten amperes, this test shall be at 25 per cent overload instead 
of 50 per cent. 

When slowly turned "on" and "off" at a rate not to ex- 
ceed ten times per minute, while carrying the rated current, 
at rated voltage, must "make" and "break" the circuit six 
thousand times before failing. 

t. Marking. 

Must be plainly marked, where it may be readily seen after 
the device is installed, with the name or trade-mark of the 
maker and the current and voltage for which the switch is 
designed. 

On flush switches these markings may be placed on the sub- 
plate. On other types they must be placed on the front of 
the cap, cover or plate. 

Switches which indicate whether the current is "on" or 
"off" are recommended. 



66. Circuit Breakers.- 

(See Figure 190.) 

(For installation rules see Nos. 8 c, 19, 23 e and f.) 

Circuit Breakers for operation on circuits of 550 volts or 
less must be made to comply with the following specifications, 
except in those few cases where peculiar design allows the 
breaker to fulfill the general requirements in some other way, 
and where it can successfully withstand the test of Section d. 
hi such cases the breakers should be submitted for special 
examination and approval before being used. 



334 



MODERN ELECTRICAL CONSTRUCTION. 



a. Base. 

Must be mounted on non-combustible, non-absorptive, in- 
sulating bases, such as slate or marble. Bases with an area 
of over twenty-five square inches must have at least four 
supporting screws. Holes for the supporting screws must be 
so located or countersunk that there will be at least one-half 
of an inch space measured over the surface between the head 
of the screw or washer and the nearest live metal part, and 
in all cases when between parts of opposite polarity must be 
countersunk. 

b. Mounting. 

Pieces carrying contact parts must be screwed to the base 
by at least two screws, or else made with a square shoulder, 
dowel pin, or equivalent device, to prevent possible turning, 
and the nuts or screw heads on the under side of the base of 
''front connected" breakers must be countersunk not less than 




Single Pole. 



Double Pole, 



Figure 190. 



one-eighth inch, and covered with a waterproof compound 
which will not melt below 150 degrees Fahrenheit (65 degrees 
Centigrade). All breakers must be provided with easily ac- 
cessible means of tripping them by hand without injury to the 
operator. 



FITTINGS, MATERIALS, ETC. 335 

c. Breaking Capacity. 

Must successfully operate three times with two minute in- 
tervals intervening without incapacitating the breaker, the 
conditions of testing current to be as given in the following 
table :— 

Current rating Minimum avail- 
of breakers. able capacity of 

Per cent of Volt- supply system 
age drop in test not including 

circuit with rated overload capacity, 
current flowing. 
o to ioo Amp. 2 i,ooo Amp. 

ioi to 300 Amp. 3 3,000 Amp. 

400 Amp. 4 4,000 Amp. 

500 Amp. 5 5,ooo Amp. 

No filing of contacts or other repairing of the breaker to be 
made during the test. 

Multiple breakers must comply with above requirements 
whether the test is on all poles at once or on one pole in- 
dividually. 

d. Voltage Test. 

Must successfully withstand 2,000 volts A. C. for one min- 
ute between live metal and ground, between poles in multi- 
polar breaker, and between terminals with breaker open. 

e. Carrying Capacity. 

The maximum rise in temperature at rated current must 
not exceed 50 degrees Centigrade (90 degree Fahrenheit) 
for coils, or 30 degrees Centigrade (54 degrees Fahrenheit) 
for other parts. 

/. Calibration. 

Must not have a plus or minus error greater than 10 per 
cent at any point of its calibration. 

g. Mechanism. 

Metal work of automatic over load circuit breakers must 
be substantial in construction, and must have ample metal for 
stiffness. The contact parts shall be arranged so that thor- 



33^ MODERN ELECTRICAL CONSTRUCTION. 

oughly good bearings are obtained; the entire device must be 
mechanically well made throughout. 

h. Marking. 

Must be plainly marked, where it will be visible when in- 
stalled, with the name of the maker and the current and 
voltage for which the device is designed. 

67. Cut-Outs. 

(For installation rules see Nos. 8 c, ig, 23, 25 a and 33 a.) 

These requirements do not apply to rosettes, attachment 
plugs, car lighting cut-outs, and protective devices for signal- 
ing systems. 

General Rules. 

a. Must be supported on bases of non-combustible, non- 
absorptive, insulating material. 

b. Cut-outs must be of the enclosed type, when not ar- 
ranged in approved cabinets, so as to obviate any danger of 
the melted fuse metal coming in contact with any substance 
which might be ignited thereby. 

c. Cut-outs must operate successfully on short-circuits, 
under the most severe conditions with which they are liable 
to meet in practice, at 25 per cent above their rated voltage, 
and for link fuse cut-outs with fuses rated at 50 per cent above 
the current for which the cut-out is designed, and for enclosed 
fuse cut-outs with the largest fuses for which the cut-out is 
designed. 

With link fuse cut-outs there is always the possibility of a larger 
fuse being put into the cut-out than it was designed for, which is 
not true of enclosed fuse cut-outs classified as required under Sec- 
tion 0. Again the voltage in most plants can, under some condi- 
tions, rise considerably above the normal. The need of some mar- 
gin as a factor of safety to prevent the cut-outs from being ruined 
in ordinary service, is therefore evident. 

The most severe service which can be required of a cut-out 
in practice is to open a "dead short-circuit," with only one fuse 
blowing, and it is with these conditions that all tests should be 
made. (See Section i.) 

d. Must be marked where it will be plainly visible when 
installed with the name of the maker, and current and voltage 
for which the device is designed. 



FITTINGS, MATERIALS, ETC. 



337 



Link-Fuse Cut-Outs. 
(Cut-outs of porcelain are not approved for link fuses.) 

The following rules are intended to cover open link fuses 
mounted on slate or marble bases, including switchboards, tablet- 
boards and single fuse-blocks. They do not apply to fuses mounted 
on porcelain bases, to the ordinary , porcelain cut-out blocks, en- 
closed fuses, or any special- or covered type of fuse. When tablet- 
boards or single fuse-blocks with such open link fuses on them are 
used in general wiring, they must be enclosed in cabinet boxes 
made to meet the requirements of No. 70. This is necessary, be- 
cause a severe flash may occur when such fuses melt, so that 
they would be dangerous if exposed in the neighborhood of any 
combustible material. 

e. Base. 

(See Figures 191 and 192.) 

Must be mounted on slate or marble bases. Bases with an 
area of over twenty-five square inches must have at least 
four supporting screws. Holes for supporting screws must 





Figure 191. 



Figure 192. 



be kept outside of the area included by the outside edges of 
the fuse-block terminals, and must be so located or counter- 
sunk that there will be at least one-half of an inch space, 
measured over the surface, between the head of the screw or 
washer and the nearest live metal part. 

/. Mounting. 

Nuts or screw heads on the under side of the base must 
be countersunk not less than one-eigTith inch, and covered 



338 MODERN ELECTRICAL CONSTRUCTION. 

with a waterproof compound which will not melt below 150 
degrees Fahrenheit (65 degrees Centigrade). 

g. Metal. 

All fuse-block terminals must have ample metal for stiff- 
ness and to prevent rise in temperature of any part of over 
50 degrees Fahrenheit (28 degrees Centigrade) at full load. 
Terminals, as far as practicable, should be made of compact 
form instead of being rolled out in thin strips, and sharp 
edges or thin projecting pieces, as on wing thumb nuts and 
the like, should be avoided. Thin metal, sharp edges and pro- 
jecting pieces are much more likely to cause an arc to start 
than a more solid mass of metal. It is a good plan to round 
all corners of the terminals and to chamfer the edges. 

h. Connections. 

Clamps for connecting the wires to the fuse-block ter- 
minals must be of solid, rugged construction, so as to insure 
a thoroughly good connection and to withstand considerable 
hard usage. For fuses rated at over thirty amperes, lugs firmly 
screwed or bolted to the terminals and into which the conduct- 
ing wires are soldered must be used. 

See note under No. 65 h. 

i. Test. 

Must operate successfully when blowing only one fuse at 
a time on short-circuits with fuses rated at 50 per cent above 
and with a voltage 25 per cent above the current and voltage 
for which the cut-out is designed. 

/. Spacings. 

Spacings must be at least as great as those given in the 
following table, which applies only to plain, open link-fuses 
mounted on slate or marble bases. The spaces given are cor- 
rect for fuse-blocks to be used on direct-current systems, 
and can therefore be safely followed in devices designed for 
alternating currents. If the copper fuse-tips overhang the 
edges of the fuse-block terminals, the spacings should be meas- 
ured between the nearest edges of the tips. 



FITTINGS, MATERIALS, ETC. 



339 



Minimum Separa- 
tion of Nearest 
Metal Parts of 
Opposite Polarity. 



Not over 123 Volts: 

10 amperes or less 
11- 100 amperes 
101- 300 amperes 
301-1,000 amperes 
Not over 230 Volts: 
10 amperes or less 
11- 100 amperes 
101- 300 amperes 
301-1,000 amperes 



V4 


inch 


1 


inch 


1 


inch 


i54 


inch 


1V2 


inch 


i?4 


inch 


2 


inch 



inch 



Minimum 
Break- 
Distance. 



54 inch 
Ya inch 

1 inch 

154 mcn 

1% inch 
i^4 inch 
1^2 inch 

2 inch 



A space must be maintained between fuse terminals of the same 
polarity of at least one-half inch for voltages up to 125 and of at 
least three-quarter inch for voltages from 126 to 250. This is the 
minimum distance allowable, and greater separation should be 
provided when practicable. 

For 250 volt boards or blocks with the ordinary front-connected 
terminals, except where these have a mass of compact form, equiv- 
alent to the back-connected terminals usually found in switch- 
board work, a substantial barrier of insulating material not less 
than one-eighth of an inch in thickness, must be placed in the 
"break" gap — this barrier to extend out from the base at least one- 
eighth of an inch farther than any bare live part of the fuse- 
block terminal, including binding screws, nuts and the like. 

For three-wire systems cut-outs must have the break-distance re 
quired for circuits of the potential of the outside wires. 



Enclosed-Fuse Cut-Outs — Plug and Cartridge Type. 
k. Base. 

(See Figure 193.) 

Must be made of non-combustible, non-absorptive, insulat- 
ing material. Blocks with an area of over twenty-five square 
inches must have at least four supporting screws. Holes for 
supporting screws must be so located or countersunk that 
there will be at least one-half of an inch space, measured over 
the surface, between the screw-head or washer and the near- 
est live metal part, and in all cases when between parts of 
opposite polarity must be countersunk. 



34° 



MODERN ELECTRICAL CONSTRUCTION. 



/. Mounting. 

Nuts or screw-heads on the under side of the base must 
be countersunk at least one-eighth of an inch and covered with 
a waterproof compound which will not melt below 150 de- 
grees Fahrenheit (65 degrees Centigrade). 

m. Terminals. 

Except for sealable service and meter cut-outs, terminals 
must be of either the Edison plug, spring clip or knife blade 
type, of approved design, to take the corresponding standard 






Figure 193. 

enclosed fuses. They must be secured to the base by two 
screws or the equivalent, so as to prevent them from turning, 
and must be so made as to secure a thoroughly good contact 
with the fuse. End stops must be provided to insure the 
proper location of the cartridge fuse in the cut-out. 



n. Connections. 

Clamps for connecting wires to the terminals must be of 
a design which will insure a thoroughly good connection, and 
must be sufficiently strong and heavy to withstand consider- 
able hard usage. For fuses rated to carry over thirty am- 
peres, lugs firmly screwed or bolted to the terminals and into 
which the connecting wires shall be soldered must be used. 



FITTINGS, MATERIALS, ETC. 341 

o. Classification. 

Must be classified as regards both current and voltage as 
given in the following table, and must be so designed that the 
bases of one class cannot be used with fuses of another class 
rated for a higher current or voltage. 

Standard Plug or Cartridge Cut-Outs. 

Not over 250 Volts: Not over 600 Volts: 

o- 30 amperes. o- 30 amperes. 

31- 60 amperes. 31- 60 amperes. 

61-100 amperes. 61-100 amperes. 

101-200 amperes. 101-200 amperes. 

201-400 amperes. 201-400 amperes. 
401-600 amperes. 

Sealable Service and Meter Cut-Outs, 

Not over 250 Volts: Not over 600 Volts: 
o- 30 amperes. o- 30 amperes. 

31- 60 amperes. 31- 60 amperes. 

61-100 amperes. 61-100 amperes. 

101-200 amperes. 101-200 amperes. 

p. Design. 

Must be of such a design that it will not be easy to form 
accidental short circuits across live metal parts of opposite 
polaritv on the block or on the fuses in the block. 
68. Fuses. 

(For installation rules, see Nos. 19 and 23.) 

Link Fuses. 

(See Figure 194.) 
a. Terminals. 

Must have contact surfaces or tips of harder metal, hav- 
ing perfect electrical connections with the fusible part of the 
strip. 

The use of the hard metal tip is to afford a strong mechanical 
bearing for the screws, clamps or other devices provided for hold- 
ing the fuse. 



342 MODERN ELECTRICAL CONSTRUCTION. 

b. Rating. 

Must be stamped with about 80 per cent of the maximum 
current which they can carry indefinitely, thus allowing about 
25 per cent overload before the fuse melts. 

With naked open fuses, of ordinary shapes and with not over 
500 amperes capacity, the minimum current which will melt them 
in about five minutes may be safely taken as the melting point, as 
the fuse practically reaches its maximum temperature in this time. 
With larger fuses a longer time is necessary. This data is given 
to facilitate testing. 

c. Marking. 

Fuse terminals must be stamped with the maker's name 
or initials, or with some known trade-mark. 

Enclosed Fuses — Plug and Cartridge Type. 

These requirements do not apply to fuses for rosettes, at- 
tachment plugs, car-lighting cut-outs and protective devices 
for signaling systems. 

d. Construction. 

The fuse casing must be sufficiently dust-tight so that lint 




Figure 194. 

and dust cannot collect around the fusible wire and become 
ignited when the fuse is blown. 

The fusible wire must be attached to the terminals in such 
a way as to secure a thoroughly good connection and to make 
it difficult for it to be replaced when melted. 

e. Classification. 

Must be classified to correspond with the different classes 
of cut-out blocks, and must be so designed that it will be im- 



FITTINGS, MATERIALS, ETC. 343 

possible to put any fuse of a given class into a cut-out block 
which is designed for a current or voltage lower than that of 
the class to which the fuse belongs. 

/. Terminals. 

The fuse terminals must be sufficiently heavy to insure 
mechanical strength and rigidity. The styles of terminals, 
except for use in sealable service and meter cut-outs, must be 
as follows : — 

Not over 250 Volts: 

A. Cartridge fuse (ferrule contact). 

B. Approved plugs for Edison cut-outs not ex- 
0-30 Amps. -j ceeding 125 volts, but including 3-wire cir- 
cuits with grounded neutral and 250 volts 
between outside wires. 



31-60 Amps. { Cartrid » e fuse 



(ferrule contact). 

61-100 Amps. ) 
101-200 Amps. ( ., , , _ . ,. .. .. _ 
201-400 Amps. ( Cartridge fuse (knife blade contact). 

401-600 Amps. ) 

Not over 600 Volts: 
31-60 Amps. } Cartridge fuse (ferrule contact). 

61-100 Amps. ) 
101-200 Amps. \ Cartridge fuse (knife blade contact). 
201-400 Amps. ) 



g. Dimensions. 

Cartridge enclosed fuses and corresponding cut-out blocks, 
except for sealable service and meter cut-outs, must conform 
to the dimensions given in the table attached. 



344 



MODERN ELECTRICAL CONSTRUCTION. 



TABLE OF DIMENSIONS OF THE 
STANDARD CARTRIDGE 




STYLE OF TERMINAL FORCARTRIDGE FUSES 
* 0-60 AMPERES 




Form 1. CARTRIDGE FUSE— Ferrule Contact. 





Rated 
Capacity. 

Amperes. 


A 


B 


C 


Voltage. 


Length 

over 

Terminals. 

Inches. 


Distance 

between 

Contact 

Clips 

Inches. 


Width 

of 

Contact 

Clips. 

Inches. 


Not over 
250 


0-30 
31-60 


a 2 
s 3 


1 
1% 


y 2 

% 


- 


61-100 
101-200 
201-400 
401-600 


a 7y 8 

S 8% 
fa 10% 


4 

4V 2 

5 

6 


7 /8 

1% 

1% 

2y 8 


Not over 
600 


0-30 
31-60 


r-l 

a 5 

S 5% 

fa 


4 

4V 4 


x / 2 

% 




61-100 
101-200 
201-400 


| 9% 

o H% 
fa 


6 

7 
8 


% 

154 

1% 



FITTINGS, MATERIALS, ETC. 



345 



NATIONAL ELECTRICAL CODE 
ENCLOSED FUSE 



<— c-J 



X 



1 



STYLE OF TERMINAL FOR CARTRIDGE F 

fil-fiOO AMPE.RCS 



usfs| 




Form 2. CARTRIDGE FUSE— Knife Blade Contact. 



D 


E 


F 


G 




Diameter of 

Ferrules or 

Thickness 

of Terminal 

Blades. 

Inches. 


Min. Length 
of Ferrules 
or of Termi- 
nal Blades 
outside of 
Tube. 
Inches 


Dia. 

of 

Tube. 

Inches. 


Width 

of 

Terminal 

Blades. 

Inches. 


Rated 
Capacity. 

Amperes. 


It 


y 2 
% 


y 2 


iH 

a 

o 

fa 


0-30 
31-60 


A 

V4 


i 

i% 
i% 

2K 


i 

iy 2 

2 

2Mj 


1% a 

i% s 

2 fa 


61-100 
101-200 
201-400 
401-600 




y 2 

% 


1 


a 

b 

O 
fa 


0-30 
31-60 


y 8 

A 


i 

i% 

i% 


154 

i% 

2y 2 


1% | 

1% g 


61-100 
101-200 
201-400 



346 MODERN ELECTRICAL CONSTRUCTION. 

h. Rating. 

Fuses must be so constructed that with the surrounding 
atmosphere at a temperature of 75 degrees Fahrenheit (24 
degrees Centigrade) they will carry indefinitely a current 10 
per cent greater than that at which, they are rated, and at a 
current 25 per cent greater than the rating, they will open 
the circuit without reaching a temperature which will injure 
the fuse tube or terminals of the fuse block. With a current 
50 per cent greater than the rating and at room tempera- 
ture of 75 degrees Fahrenheit (24 degrees Centigrade), the 
fuses starting cold, must blow within the time specified 
below : — 

0-30 Amperes I minute 

31-60 Amperes 2 minutes 

61-100 Amperes 4 minutes 

101-200 Amperes 6 minutes 

201-400 Amperes 12 minutes 

401-600 Amperes 15 minutes 

i. Marking. 

Must* be marked, where it will be plainly visible, with the 
name or trade-mark of the maker, the voltage and current 
for which the fuse is designed, and the words "National Elec- 
trical Code Standard." Each fuse must have a label, the 
color of which must be green for 250-volt fuses and red for 
600-volt fuses. 

It will be satisfactory to abbreviate tbe above designation to 
"N. E. Code St'd" where space is necessarily limited. 

/'. Temperature Rise. 

The temperature of the exterior of the fuse enclosure must 
not rise more than 125 degrees Fahrenheit (70 degrees Centi- 
grade) above that of the surrounding air when the fuse is 
carrying the current for which it is rated. • 

k. Test. 

Must not hold an arc or throw out melted metal or suf- 
ficient flame to ignite easily inflammable material on or near 
the cut-out when only one fuse is blown at a time on a short 
circuit on a system of the voltage for which the fuse is rated. 



FITTINGS, MATERIALS, ETC. 



347 



The normal capacity of the system must be in excess of 
the load on it just previous to the test by at least five times 
the rated capacity of the fuse under test. 

The resistance of the circuit up to the cut-out terminals 




Figure 195. 



must be such that the impressed voltage at the terminals 
will be decreased one per cent when a current of 100 amperes 
is passed between them. 

For convenience a current of different value may be used, in 
which case the per cent drop in voltage allowable would vary in 
direct proportion to the difference in current used. 



34& MODERN ELECTRICAL CONSTRUCTION. 

The above requirement regarding the capacity of the testing cir- 
cuit is to guard against making the test on a system of so small 
capacity that the conditions would be sufficiently favorable to 
allow really poor fuses to stand the test acceptably. On the 
other hand, it must be remembered that if the test is made on a 
system of very large capacity, and especially if there is but lit- 
tle resistance between the generators and fuse, the conditions may 
be more severe than are liable to be met with in practice outside 
of the large power stations, the result being that fuses entirely 
safe for general use may be rejected if such test is insisted upon. 

69. Tablet and Panel Boards. 

The following specifications are intended to apply to all panel 
and distributing boards used for the control of light and power 
circuits, but not to such switch boards in central stations, sub- 
stations or isolated plants as directly control energy derived from 
generators or transforming devices. 

(See Figure 195.) 
a. Design. 

The specifications for construction of switches and cut- 
outs (see Nos. 65 and 67) must be followed as far as they 
apply. 

In the relative arrangement of fuses and switches, the fuses 
may be placed between the bus-bars and the switches, or be- 
tween the switches and the circuits, except in the case of serv- 
ice switches, when Rule 23 a must be complied with. 

When the branch switches are between the fuses and bus- 
bars, the connections must be so arranged that the blades will 
be dead when the switches are open. 

When there are exposed live metal parts on the back of 
board, a space of at least one-half inch must be provided be- 
tween such live metal parts and the cabinet in which board 
is mounted. 

b. Spacings. 

The following minimum distance between bare live metal 
parts (bus-bars, etc.) must be maintained: — 

Between parts of opposite polarity, Between parts of 

except at switches and link fuses. same polarity. 

When mounted on When held free At link 

the same surface. in air. fuses. 

Not over 125 volts, % inch. y 2 inch. Vo inch. 

Not over 250 volts, 1% inch. % iDC'i. % inch. 

Not over 600 volts, 2 inch. 1% inch. 



FITTINGS, MATERIALS, ETC. 349 

At switches or enclosed fuses, parts of the same polarity may 
be placed as close together as convenience in handling will allow. 

It should be noted that the above distances are the minimum 
allowable, and it is urged that greater distances be adopted where- 
ever the conditions will permit. 

The spacings given in the first column apply to the branch con- 
ductors where enclosed fuses are used. Where link fuses or knife 
switches are used, the spacmgs must be at least as great as those 
required by Nos. 65 and 67. 

The spacings given in the second column apply to the distance 
between the raised main bars and between these bars and the 
branch bars over which they pass. 

The spacings given in the third column are intended to prevent 
the melting of a link fuse by the blowing of an adjacent fuse of the 
same polarity. 

Panel boards of special design in which the insulation and sepa- 
ration between bus-bars and between other current-carrying parts 
is secured by means of barriers or insulating materials instead of 
by the spacings given above, must be submitted for special examina- 
tion and approval before being used. 

c. Marking. 

Must be marked where the marking can be plainly seen 
when installed, with the name or trade-mark of the manu- 
facturer and the maximum capacity in amperes and the volt- 
age for which the board is designed. 

Figure 196 shows a view of the McWilliams "Simplicity" 
type Metering Panelboard, manufactured by the J. Lang 
Electric Co., Chicago, with six circuits. 

Figure 197 shows the same type of panelboard diagram- 
matically, with twenty circuits. 

This panelboard is designed for use in office, factory, store 
and apartment buildings where there are tenants requiring 
metered service. 

This panelboard is also used in manufacturing buildings 
where individual costs are required on the current consumed 
for different departments. 

The greater number of these panelboards are used in office 
buildings, owing to the fact that a large number of meters 
and the consequent wiring and maintenance of same is elimin- 
ated. By the use of this panelboard but one meter is required 
for each tenant irrespective of the number or combination of 
rooms occupied. With this panelboard the meters are grouped 
at one location in a central meter closet adjacent to the panel- 
board. It is now customary to run circuit wiring from this 



350 



MODERN ELECTRICAL CONSTRUCTION. 




Figure 196. 



FITTINGS, MATERIALS, ETC. 351 

central point of distribution so that one circuit operates to 
each room on the floor, or to each bay, if the building is of 
factory type. 

By the use of this panelboard with wiring of this character 
one or all of the circuits can be connected together through 
one meter. 

The panelboard shown in Figure 196 is designed for six 
meters, while the panelboard shown in Figure 197 is designed 
for twelve meters. The meter loops are fused on one polarity 
for the 2-wire meter, and on both polarities for the 3-wire 
type meter. The^ common neutral or pressure wire loops 
from meter to meter, without fusing. 

The 2-wire branch circuits are protected in the usual man- 
ner by two fuses. One main bus bar runs the full length of 
the panelboard adjacent to the fuse plug holders on either 
side of the board. To this bus bar one set of fuses are con- 
nected. The other, or adjacent set of fuses are connected 
to the numbered posts which, in turn, support the round circuit 
bars crossing the meter bars. The round circuit bar which 
crosses the meter bar contains a movable switch contactor. 
This movable switch contactor can be electrically connected 
to the meter bars at every point the round circuit bar crosses 
the meter bars. This permits the grouping of circuits in any 
combination to selected meter bars and through the desired 
meter. 

The meter bus bars are placed on edge for the purpose of 
condensing the panelboard as much as possible, and also for 
the purpose of providing a switch blade surface for the 
movable contactor to engage with. 

The meter bars are carried to proper terminal lugs at the 
top of the board for meter loop connections. 

By carefully tracing out the circuit connections in Figure 
197 it will be noted that circuits I, 2 and 3 which operate to 
rooms 1, 2 and 11 are connected to meter "B." 



352 



MODERN ELECTRICAL CONSTRUCTION. 



Q0QOI 



en 



m 



L 



in 



I 



CCTM. V CONTACTOM 




BgEECgw 

■w-ftgi --nh 



BiB *?°p 




HH 



>n 



m 



[QSOSl 



ra 



Figure 19 7. 



FITTINGS, MATERIALS, ETC. 353 

Circuits 5 and 6 operating to rooms 3 and 13 are connected 
to meter "G" 

Circuits 4, 12 and 18 operating to rooms 12, 16 and 19 are 
connected to meter "E." 

The preceding three meters are of the 2-wire type. 
Circuits 8, 15, 16, 10, 13 and 14 operating to rooms, 14, 8, 
18, 15, 7 and 17 are connected to Meter F-G. This is a 
3-wire type meter. 




Figure 198. 

This panelboard occupies a very small amount of space and 
all wire connections are made permanently on the face of the 
panelboard. This prevents improper meter connections and 
enables the tenant to readily trace the circuits connected to 
his meter. 

This type of panelboard can be used to advantage for 
metering current owing to the fact that repeated changes in 
connection of the circuit wires to meters can be made without 
the use of loose wiring connections and the consequent fire 
hazard. 



354 MODERN ELECTRICAL CONSTRUCTION. 

70. Cabinets. 

(See Figure 198.) 

For panel and distributing boards, cut-outs and switches. 

(For installation rule see Nos. 8 d, 19 b-d, 23 c and 24 b.) 

a. Design. 

Must in all cases be so constructed as to insure ample 
strength and rigidity and be dust tight. 

The hard usage to which cabinets are often subjected, especially 
during process of installation, makes it necessary so to construct 
them that they will be strong enough to keep their shape, thus 
permitting doors to close tightly and making possible the proper in- 
stallation of wiring and conduit. 

When doors are of metal, and less than 0.109 inch (No. 
12 U. S. gage) in thickness and are not lined with insulating 
material there must be a space of at least one inch between 
the door and an enclosed fuse or any live metal part. A space 
of at least two inches must be provided between open-link 
fuses and metal, metal-lined or glass paneled doors of cabinets. 
Except as above specified there must be a space of at least 
one-half inch between the walls, back or door of any cabinet 
and any exposed live metal part. Cabinets must be deep 
enough to allow the door to be closed when switches rated 
at 30 amperes or less are in any position, and when larger 
switches are thrown open as far as their construction or in- 
stallation will permit. 

There must be a space of at least one-half inch between 
the walls and back of any cabinet and the nearest exposed 
current-carrying part. 

b. Material. 

May be either of cast or sheet metal, wood or approved 
composition. Wooden or composition cabinets must not be 
used on metal conduit, armored cable or metal moulding 
systems. 

All metal used in construction of cabinets including lin- 
ings, if any, must be thoroughly painted or otherwise treated 
to prevent corrosion. 



FITTINGS, MATERIALS, ETC. 



355 



c. Wooden Cabinets. 

Wood must be well seasoned and at least three-fourths 
inch thick and be thoroughly filled and painted, and must 
be lined with a non-combustible material. 

d. Linings. 

In all cabinets, linings of slate, marble or approved com- 
position must be at least one-fourth inch thick and firmly 
secured in place ; when metal is used for the lining it must 
be at least No. 16 U. S. gage in thickness. For lining wooden 






Figure 199. 



cabinets one-eighth inch rigid asbestos board may be used 
when firmly secured in place by screws or tacks. 

e. Composition Cabinets. 

Only approved material should be used, and in no case 
less than three-fourths of an inch in thickness. 

/. Metal Cabinets. 

If cast metal is used a thickness of at least one-eighth 
inch must be provided. Sheet metal must not be less than 



356 MODERN ELECTRICAL CONSTRUCTION. 

.0625 inch thick (No. 16 U. S. gage), and must in every 
case be of sufficient thickness or so reinforced as to comply 
with Section (a) "Design." In steel cabinets having an area 
of more than 360 square inches for any surface, or having a 
single dimension greater than 2 feet, sheet metal must be used 
at least No. 14 U. S. gage in thickness ; in those having an 
area of more than 1,200 square inches for any surface, or hav- 
ing a single dimension greater than 4^ feet, the sheet metal 
must be at least No. 12 U. S. gage in thickness. 

g. Doors. 

Must close against a rabbet or have flanges over edges so 
as to make cabinets dust tight. Hinges must be of strong 
and durable design. A substantial latch or catch must be 
provided so as to keep the door closed, and a lock may be 
used in addition to the catch if desired. 

When doors have glass panels the glass must be at least 
one-eighth inch thick (commercial thickness), and must not 
have a greater area than 450 square inches unless plate glass 
at least one-fourth inch in thickness is used. 

h. Marking. 

Must be marked with manufacturer's name where the 
name can be plainly seen when the cabinet is installed. 

71. Rosettes. 

(See Figure 199.) 

Ceiling rosettes, both fused and fuseless, must be constructed in 
accordance with the following specifications : — 

a. Base. 

Current-carrying parts must be mounted on non-com- 
bustible, non-absorptive, insulating bases. There should be no 
openings through the rosette base except those for the sup- 
porting screws and in the concealed type for the conductors 
also, and these openings should not be made any larger than 
necessary. 

There must be at least one-fourth inch space, measured 
over the surface, between supporting screws and current-carry- 



FITTINGS, MATERIALS, ETC. 357 

ing parts. The supporting screws must be so located or coun- 
tersunk that the flexible cord cannot come in contact with 
them. 

Bases for the knob and cleat type must have at least two 
holes for supporting screws ; must be high enough to keep 
the wires and terminals at least one-half inch from the surface 
to which the rosette is attached, and must have a porcelain 
lug under each terminal to prevent the rosette from being 
placed over projections which would reduce the separation to 
less than one-half inch. 

Bases for the moulding and conduit box types must be 
high enough to keep the wires and terminals at least three- 
eighths inch from the surface wired over. 

b. Mounting. 

Contact pieces and terminals must be secured in position 
by at least two screws, or made with a square shoulder, or 
otherwise arranged to prevent turning. 

The nuts or screw heads on the under side of the base must 
be countersunk not less than one-eighth inch and covered with 
a waterproof compound which will not melt below 150 de- 
grees Fahrenheit (65 degrees Centigrade). 

c. Terminals. 

Line terminal plates must be at least .06 inch in thickness, 
and terminal screws must not be smaller than No. 6 standard 
screw with about 32 threads per inch. 

Terminal plates for the flexible cord and for fuses must 
be at least .06 inch in thickness. The connection to these 
plates shall be by binding screws not smaller than No. 5 
standard screw with about 40 threads per inch. At all bind- 
ing screws for line wires and for flexible cord, up-turned 
lugs, or some equivalent arrangement, must be provided which 
will secure the wires being held under the screw heads. 

d. Cord Inlet. 

The diameter of the cord inlet hole should measure thir- 
teen thirty-seconds inch in order that standard portable cord 
may be used. 

e. Knot Space. 

Ample space must be provided for a substantial knot tied 
in the cord as a whole. 



358 MODERN ELECTRICAL CONSTRUCTION. 

All parts of the rosette upon which the knot is likely to 
bear must be smooth and well rounded. 

/. Cover. 

When the rosette is made in two parts, the cover must 
be secured to the base so that it will not work loose. 

In fused rosettes, the cover must fit closely over the base 
so as to prevent the accumulation of dust or dirt on the inside, 
and also to prevent any flash or melted metal from being 
thrown out when the fuses melt. 

g. Marking. 

Must be plainly marked where it may readily be seen after 
the rosette has been installed, with the name or trade-mark 
of the manufacturer, and the rating in amperes and volts. 
Fuseless rosettes may be rated 3 amperes, 250 volts ; fused 
rosettes, with link fuses, not over 2 amperes, 125 volts. 

h. Test. 

Fused rosettes must have a fuse in each pole and must oper- 
ate successfully when short-circuited on the voltage for which 
they are designed, the test being made with the two fuses in 
circuit. 

When link fuses are used the test shall be made with fuse wire 
which melts at about 7 amperes in one-inch lengths. The larger 
fuse is specified for the test in order to more nearly approximate 
the severe conditions obtained when only one 2-ampere fuse (the 
rating of the rosette) is blown at a time. 

Fused rosettes equipped with enclosed fuses are much preferable 
to the link fuse rosettes. 

72. Sockets. 

(See Figure 200.) 
(For installation rules, see No. 31.) 

Sockets of all kinds, including wall receptacles, must be con- 
structed in accordance with the following specifications : — 

a. Marking. 

All sockets and receptacles must be marked with the manu- 
facturer's name or trade-mark. All sockets and receptacles 
must be marked as given in the following sections. 



FITTINGS, MATERIALS, ETC. 359 

b. Ratings. 

Key Sockets. — The Standard key socket (any socket hav- 
ing Standard Edison screw shell and ordinary "slow make" 
switch) to be rated 250 watts, 250 volts. 

Marking may be 250 W., 250 V. This rating shall not be 
interpreted to permit the use, at any voltage, of current above 
2}/2 amperes on any standard key or pull socket. 

A key socket with Standard Edison shell and special switch 
which "makes" and "breaks" with a quick snap and does not 
stop when motion has been once imported by the button or 
handle, may be rated 660 watts, 250 volts (660 W., 250 V.). 

Miniature and Candelabra key sockets to be rated 75 watts, 
125 volts (75 W., 125 V.). 

Keyless Sockets. — Standard keyless sockets with Standard 
Edison screw shell to be rated 660 watts, 250 volts (660 W., 
2 50 V.). This rating shall not be interpreted to permit the 
use, at any voltage, of current above 6 amperes on any key- 
less socket. 

Weatherproof sockets with Standard Edison shell and hav- 
ing no exposed current carrying parts may be rated 660 watts, 
600 volts (660 W., 600 V.). 

Miniature and Candelabra keyless sockets to be rated 75 
watts, 125 volts (75 W., 125 V.). 

Double Ended Sockets. — Each Edison screw shell to be 
rated at 250 watts, 250 volts for key type, 660 watts, 250 volts 
for keyless type, the devices being marked with a single mark- 
ing applying to each lamp holder. 

These ratings shall not be interpreted to permit the use 
at any voltage, of current above 2^ amperes for key type, or 
above 6 amperes for keyless types. 

c. Shell. 

Metal used for shells must be moderately hard, but not 
hard enough to be brittle or so soft as to be easily dented or 
knocked out of shape. Brass shells must be at least thirteen 
one-thousandths of an inch in thickness, and shells of any 
other material must be thick enough to give the same stiffness 
and strength as the required thickness of brass. 

d. Lining. 

The inside of the shells must be lined with insulating ma- 
terial, which must absolutely prevent the shell from becoming 



?60 MODERN ELECTRICAL CONSTRUCTION. 

a part of the circuit, even though the wires inside the sockets 
should become loosened or detached from their position under 
the terminal screws. 

The material used for lining must be at least one thirty- 
second of an inch in thickness, and must be tough and tena- 
cious. It must not be injuriously affected by the heat from 
the largest lamp permitted in the socket, and must leave water 
in which it is boiled practically neutral. It must be so firmly 
secured to the shell that it will not fall out with ordinary 
handling of the socket. It is preferable to have the lining 
in one piece. 

The cap must also be lined, and this lining must comply with 
the requirements for shell linings. 

The shell lining should extend beyond the shell far enough so that 
no part of the lamp base is exposed when a lamp is in the socket. 




Figure 200. 

The standard Edison lamp base measures fifteen-sixteenths inches 
in a vertical plane from the bottom of the center contact to the 
upper edge of the screw shell. 

In sockets and receptacles of standard forms a ring of any mate- 
rial inserted between an outer metal shell of the device and the in- 
ner screw shell for insulating purposes and separable from the de- 
vice as a whole, is considered an undesirable form of construction. 
This does not apply to the use of rings in lamp clusters or in 
devices where the outer shell is of porcelain, where such rings serve 
to hold the several porcelain parts together, and are thus a nec- 
essary part of the whole structure of the device. 

e. Cap. 

Caps, when of sheet brass, must be at least thirteen one- 
thousandths of an inch in thickness, and when cast or made 
of other metals must be of equivalent strength. The inlet 
piece, except for special sockets, must be tapped with a stand- 
ard one-eighth inch pipe thread. It must contain sufficient 
metal for a full, strong thread, and when not in one piece with 
the cap, must be joined to it in, such a way as to give the 
strength of a single piece. 



FITTINGS, MATERIALS, ETC. 3^1 

There must be sufficient room in the cap to enable the or- 
dinary wireman to easily and quickly make a knot in the cord 
and to push it into place in the cap without crowding. All 
parts of the cap upon which the knot is likely to bear must 
be smooth and well insulated. 

The cap lining called for in the note to Section d will provide a 
sufficiently smooth and well-insulated surface for the knot to bear 
upon. 

Sockets with an outlet threaded for three-eighths-inch pipe will, 
of course, be approved where circumstances demand their use. 
This size outlet is necessary with most stiff pendants and for the 
proper use of reinforced flexible cord, as explained in the note to 
No. 32 d. 

f. Frame and Screws. 

The frame which holds the moving parts must be suf- 
ficiently heavy to give ample strength and stiffness. 

Brass pieces containing terminal screws must be suf- 
ficiently heavy to give ample strength and stiffness, and have 
at least six one-hundreths of an inch of thread for terminal 
screws. 

Terminal post screws must not be smaller than No. 5 
standard screw, with about forty threads per inch. 

g. Spacing. 

Points of opposite polarity must everywhere be kept not 
less than three sixty-fourths of an inch apart, unless sepa- 
rated by a reliable insulation. 

K Connections. 

The connecting points for the flexible cord must be made 
to very securely grip a No. 16 or 18 B. & S. gage conductor. 
An up-turned lug, arranged so that the cord may be gripped 
between the screw and the lug in such a way that it cannot 
possibly come out, is strongly advised. 

i. Lamp Holder. 

The socket must firmly hold the lamp in place so that it 
cannot be easily jarred out and must provide a contact good 
enough to prevent undue heating with the maximum current 
allowed. The holding pieces, springs and the like, if a part 



362 MODERN ELECTRICAL CONSTRUCTION. 

of the circuit, must not be sufficiently exposed to allow them 
to be brought in contact with anything outside of the lamp 
and socket. 

/. Base. 

The base on which current carrying parts are mounted 
must be of porcelain and all insulating material used must be 
of approved material. 

k. Key. 

The socket key-handle must be of such a material that it 
will not soften from the heat of a fifty candle-power lamp 
hanging downwards from the socket in air at 70 degrees 
Fahrenheit (21 degrees Centigrade), and must be securely, 
but not necessarily rigidly, attached to the metal spindle 
which it is designed to turn. 

/. Sealing. 

All screws in porcelain pieces, which can be firmly sealed 
in place, must be so sealed by a waterproof compound which 
will not melt below 200 degrees Fahrenheit (93 degrees Centi- 
grade). 

m. Putting Together. 

The socket as a whole must be so put together that it will 
not rattle to pieces. Bayonet joints or an equivalent are rec- 
ommended. 

n. Test. 

The socket when slowly turned "on and off" at a rate not 
to exceed ten times per minute, while carrying a load of one 
ampere at 250 volts, must "make" and "break" the circuit 
6,000 times before failing and must operate successfully at 50 
per cent overload in amperes at both 125 and 250 volts direct 
current under the most severe conditions which they are liable 
to meet in practice. 

0. Keyless Sockets. 

Keyless sockets of all kinds must comply with the re- 
quirements for key sockets as far as they apply. 



FITTINGS, MATERIALS, ETC. 363 

/>. Sockets of Insulating Material. 

Sockets made of porcelain or other insulating material 
must conform to the above requirements as far as they apply, 
and all parts must be strong enough to withstand a moderate 
amount of hard usage without breaking. 

Porcelain shell sockets being subject to breakage, and constitut- 
ing a hazard when broken, will not be accepted for use in places 
where they would be exposed to hard usage. 
q. Inlet Bushing. 

When the socket is not attached to a fixture, the threaded 
inlet must be provided with a strong insulating bushing 
having a smooth hole at least nine thirty-seconds of an inch 
in diameter. The edges of the bushing must be rounded 





Figure 201. 

and all inside fins removed, so that in no place will the cord 
be subjected to the cutting or wearing action of a sharp edge. 
Bushings for sockets having an outlet threaded for three-eighths- 
inch pipe should have a hole thirteen thirty-seconds of an inch 
in diameter, so that they will accommodate approved reinforced 
flexible cord. 

73. Hanger-Boards for Series Arc Lamps. 

(See Figure 201.) 
(For installation rules: see Nos. 21 d and 22 b.) 
a. Hanger-boards must be so constructed that all wires 
and current-carrying devices thereon will be exposed to view 
and thoroughly insulated by being mounted on a non-com- 
bustible, non-absorptive, insulating substance. All switches 
attached to the same must be so constructed that they shall 
be automatic in their action, cutting off both poles to the 
lamp, not stopping between points when started and pre- 
venting an arc between points under all circumstances. 



364 MODERN ELECTRICAL CONSTRUCTION. 

74. Arc Lamps. 

(See Figure 202.) 
(For installation rules see Nos. 21 and 33.) 

a. Must be provided with reliable stops to prevent car- 
bons from falling out in case the clamps become loose. 

b. All exposed parts must be carefully insulated from 
the circuit. 




Figure 202. 



c. Must, for constant-current systems, be provided with an 
approved hand switch, and an automatic switch that will 
shunt the current around the carbons, should they fail to feed 
properly 

The hand switch to be approved, if placed anywhere ex- 
cept on the lamp itself, must comply with requirements for 
switches on hanger-boards as laid down in No. 73. 

d. Terminals must be designed to secure a thoroughly 
good and permanent contact with the supply wires, which 
contact must not become loosened by motion of the lamp 
during trimming. 



FITTINGS, MATERIALS, FTC. 3^5 

75. Spark Arresters. 

(See Figure 202.) 

(For installation rules see Nos. 21 c and 33 c.) 

a. Spark" arresters must so close the upper orifice of the 
globe that it will be impossible for any sparks, thrown off 
by the carbons, to escape. 

76. Insulating Joints. 

(For installation rules, see No. 30 a.) 

a. Must be entirely made of material that will resist the 
action of illuminating gases and will not give way or soften 
under the heat of an ordinary gas flame or leak under a 
moderate pressure. Must be so arranged that a deposit of 
moisture will not destroy the insulating effect ; must show a 
dielectric strength between gas-pipe attachments 'sufficient 
to resist throughout five minutes the application of an elec- 
tro-motive force of 4,000 volts; and must be sufficiently 
strong to resist the strain to which they are liable to be sub- 
jected during installation. 

Insulating joints having soft rubber in their construction will 
not be approved. 

77. Fixtures. 

(For installation rules, see Nos, 24 e, and 26 v to y. For con- 
struction of Wires, see No. 55J 

a. Material. 

Must be of metal or hard wood, except that other approved 
material may be used if re-enforced by metal or otherwise 
constructed to secure requisite mechanical strength. 

In all cases mechanical strength must be secured practically 
equivalent to an all-metal fixture of similar size and form. 

b. Assembly. 

All arms must be reliably secured to prevent turning. Arms 
of threaded tubing must not be lighter than No. 18 B. & S. 
gage, and with screw joints of arms there must be not less 
than five threads all engaging. All methods of fastening arms 



366 MODERN ELECTRICAL CONSTRUCTION. 

or making joints between metal parts by soldering, brazing 
or otherwise, must be such as to secure in every case ample 
strength and reliability. 

c. Sockets. 

Must, except on pendant cords, be attached to the metal 
of the fixtures and must be secured in a reliable and permanent 
manner. 

Receptacles having exposed terminals must not be used in 
canopies or in any part of fixtures unless completely enclosed 
in metal. 

d. Wireways. 

All burrs, fins and sharp edges liable to injure wire cover- 
ings must, where practicable, be removed or rounded, but in 
every case it must be possible to pull in and also to withdraw 
the wires without injuring them. Where supply wires enter 
fixture stems or casings there must be suitable fittings having 
smooth rounded edges to prevent injury to the wire coverings. 

In non-metallic fixtures wireways must be metal-lined un- 
less approved armored conductors with suitable fittings are 
used. 

On chains or similar parts where conductors are not com- 
pletely enclosed in metal, wires must be stranded and must 
have rubber insulation not less than one thirty-second inch 
in thickness or approved pendant or portable cord may be 
used. 

e. Markings. 

Must be marked with the manufacturer's name or trade- 
mark. 

/. Test. 

Must be tested in an approved manner for short circuits 
between conductors and for contacts between conductors and 
metal parts of fixtures. 

78. Rheostats, Resistance Boxes and Equalizers. 

(For installation rules, see Nos. 4 a and 8 c.) 

a. Materials. 

Must be made entirely of non-combustible materials, except 
such minor parts as handles, magnet insulation, etc. All seg- 



FITTINGS, MATERIALS, ETC. 36? 

ments, lever arms, etc., must be mounted on non-combustible, 
non-absorptive, insulating material. 

Rheostats used in dusty or linty places or where exposed to fly- 
ings of combustible material, must be so constructed that even 
if the resistive conductor be fused by excessive current, the arc 
or any attendant flame will be quickly and safely extinguished. 
Rheostats used in places where the above conditions do not exist 
may be of any approved type. 

Wood or other suitable material may be used for parts of the 
casings or covers of drum controllers, providing these parts are 
properly lined or treated with fire-resisting materials, and so ar- 
ranged that should the combustible parts within the casing be ig- 
nited, the fire would be confined within the casing or cover. 

In drum controllers and apparatus of like nature where the con- 
trolling mechanism is entirely enclosed in a substantial tight metal 
case or compartment, hard wood or other suitable material may be 
used for bases for mounting current'-carrying parts, or for other 
parts which cannot readily be made of non-combustible material, 
provided such combustible material is present only in such amount 
and so disposed that, even if it be totally destroyed by fire or ex- 
cessive heat, the effect shall be confined to the interior of the case. 

b. Construction. 

Must be so constructed that when mounted on a plane sur- 
face the casing will make contact with such surface only at the 
points' of support. An air space of at least one-fourth inch 
between -the rheostat casing and the supporting surface will be 
required. 

The construction throughout must be heavy, rugged and 
thoroughly workmanlike. 

c. Connections. 

Clamps for connecting wires to the terminals must be of a 
design which will insure a thoroughly good connection, and 
must be sufficiently strong and heavy to withstand consider- 
able hard usage. For currents above fifty amperes, lugs firmly 
screwed or bolted to the terminals, and into which the connect- 
ing wires shall be soldered, must be used. 

Clamps or lugs will not be required when leads designed for 
soldered connections are provided. 

d. Marking. 

Must be plainly marked, where it may be readily seen after 
the device is installed, with the rating and the name of the 
maker; and the terminals of motor-starting rheostats must be 
marked to indicate to what part of the circuit each is to be 
connected, as "line/ 5 "armature" and "field." 



368 MODERN ELECTRICAL CONSTRUCTION. 

e. Contacts. 

The design of the fixed and movable contacts and. the re- 
sistance in each section must be such as to secure the least 
tendency toward arcing and roughening of the contacts, even 
with careless handling or the presence of dirt. 

In motor-starting rheostats, the contact at which the cir- 
cuit is broken by the lever arm when moving from the running 
to the starting position, must be so designed that there will be 
no detrimental arcing. The final contact, if any, on which 
the arm is brought to rest in the starting position must have 
no electrical connection. 

Experience has shown that sharp edges and segments of thin 
material help to maintain an arc, and it is recommended that 
these be avoided. Segments of heavy construction have a con- 
siderable cooling effect on the arc, and rounded corners tend to 
spread it out and thus dissipate it. 

It is recommended that the circuit-breaking contacts be so con- 
structed as to "break" with a quick snap, independently of the 
slowness of movement of the operator's hand, or that a magnetic 
blowout or equivalent device be used. For dial type rheostats the 
movable contact should be flexible in a plane at right angles to the 
plane of its movement, and for medium and larger sizes the sta- 
tionary contacts should be readily renewable. 

/. No-Voltage Release. 

Motor-starting rheostats must be so designed that the con- 
tact arm cannot be left on intermediate segments, and for di- 
rect current circuits must be provided with an automatic device 
which will interrupt the supply circuit before the speed of the 
motor falls to less than one-third of its normal value. In 
motor starting rheostats for alternating current circuits the au- 
tomatic interrupting device may be omitted. 

g. Overload Release. 

Overload release devices which are inoperative during the 
process of starting a motor will not be approved, unless other 
circuit-breakers or fuses are installed in connection with them. 

If, for instance, the over-load release device simply releases the 
starting arm and allows it to fly back and break the circuit, it is 
inoperative while the arm is being moved from the starting to 
the running position. 

h. Test. 

Must, after ioo operations under the most severe normal 
conditions for which the device is designed, show no serious 



FITTINGS, MATERIALS, ETC. 369 

burning of the contacts or other faults, and the release mechan- 
ism of motor-starting rheostats must not be impaired by such 
a test. 

Field rheostats, or main-line regulators intended for con- 
tinuous use, must not be burned out or depreciated by carry- 
ing the full normal current on any step for an indefinite period. 
Resistances intended for intermittent use (such as on electric 
cranes, elevators, etc.) must be able to carry their rated cur- 
rent on any step for as long a time as the character of the 
apparatus which they control will permit them to be used con- 
tinuously. 

Starting duty resistances shall either be so constructed that 
if the resistance conductor be fused the arc, or any attendant 
flame or molten droppings, shall be confined within the rheo- 
stat ; or they shall be constructed with such capacity that when 
the rated full-load current is passed through the entire re- 
sistance for a period of five minutes there shall be no result- 
ant flaming, or molten droppings. 

Continuous duty resistances shall either be so constructed 
that if the resistive conductor be fused the arc or any at- 
tendant flame or molten droppings shall be confined within the 
rheostat or they shall be constructed with such capacity that 
if subjected to a current flow throughout the entire rheostat, 
25 per cent in excess of that at which they are rated, for a 
period of two hours, there shall be no resultant flaming or 
molten droppings. 

79. Auto-Starters. 

(For installation rules see No. 8 d.) 

Construction and Test of Auto-starters Ranging to a Maxi- 
mum of ioo Horse Power and 3,500 Volts. 

Under this class are included all such devices for starting 
A. C. Motors as employ transformer windings whereby the 
potential impressed upon the motor terminals during process 
of starting may be made less than the full line voltage and 
which have switching devices for accomplishing this result. 

Apparatus designed for starting A. C. Motors by employ- 
ing ohmic resistance coils are to be judged under No. 78— 
Rheostats. 



3/0 MODERN ELECTRICAL CONSTRUCTION. 

a. Construction. 

Coils and switches of auto-starters used in dusty and linty 
places or where exposed to flyings of combustible material, 
must be completely enclosed in substantial metal cases so 
constructed as to effectually exclude ordinary dust, lint or 
flyings of combustible material. 

Auto-starters used in places where the above conditions 
do not exist, may be of any approved type. 

Cases for either transformer coils or switches must pro- 
vide for access to the interior for inspection and for renewal 
of oil, and must be so constructed that when mounted on a 
plain surface the casing will make contact with such surface 
only at points of support. An air space at least one-fourth 
of an inch between the casing and supporting surface will be 
required. 

The oil tank shall be marked in a suitable manner to in- 
dicate the proper oil level. 

The switch must provide an off position, or running posi- 
tion and at least one starting position. It must be so ar- 
ranged that it will be held in off and running positions but 
cannot be left in a starting position or without the proper 
running overload protective devices in the circuit. 

The construction throughout must be thoroughly 
substantial. 

b. Connections. 

Clamps for connecting wires to the terminal board must 
be of a design which will insure a thoroughly good connec- 
tion and must be sufficiently strong and heavy to withstand 
considerable hard usage. For currents above 50 amperes, 
lugs firmly screwed or bolted to the terminal boards, and into 
which the connecting wires shall be soldered, must be used. 
Clamps or lugs will not be required when leads designed for 
soldered connections are provided. 

c. Marking. 

Must be plainly marked, where it may be readily seen 
after the device is installed, with the rating and name of the 
maker; terminals to be so marked as to indicate to what part 
of the circuit each is to be connected. 



FITTINGS, MATERIALS, ETC. 371 

d. Insulation Test. 

The insulation of the completely assembled apparatus 
must withstand for one minute a potential test between live 
metal parts and frame core and case as follows : — 

Rated Terminal Voltage Testing 

of Circuit. Voltage. 

Not exceeding 400 volts 1,500 volts 

401-800 2,000 volts 

&)i-i,200 3,5oo volts 

1,201-2,500 5,ooo volts 

2,500 up Double normal rated Voltages 

e. Tests. 

With full line voltage applied to line terminals and cur-' 
rent taken from taps giving between 40 and 60 per cent of 
the normal line voltage, 300 per cent of full load' current of 
the motor applied for the first fifteen seconds of each four- 
minute period for one hour must show no resultant flaming 
or molten droppings. The oil, if any, in which the trans- 
former windings are immersed shall not overflow the contain- 
ing case and the entire starter shall be practically uninjured. 

80. Reactive Coils and Condensers. 

a. Reactive coils must be made of non-combustible ma- 
terial, mounted on non-combustible bases and treated, in gen- 
eral, as sources of heat. 

b. Condensers must be treated like other apparatus oper- 
ating with equivalent voltage and currents. They must have 1 
non-combustible cases and supports, and must be isolated 
from all combustible materials and, in general, treated as 
sources of heat. 

81. Transformers. 

(For installation rules see Nos. 11 , 14, 15, 36 and 45.) 

a. Must not be placed in any but metallic or other non- 
combustible cases. 

It is advised that every transformer with either primary or 
secondary voltages over 550 volts to be so designed and connected 
that the middle point of the secondary coil can be reached, if, at 
any future time, it should be desired to ground it. 



2^2 MODERN ELECTRICAL CONSTRUCTION. 

b. Must be plainly marked where it may be readily seen 
after the transformer is installed, with the name of the maker, 
with the primary and secondary voltages and the rated 
capacity. 

c. Must be constructed to comply with the following 
tests : — 

1. Shall be run for a sufficient time to reach a prac- 

tically constant temperature at full rated load, and 
at the end of that time a rise in temperature, as 
measured by the increase in resistance of the 
windings, shall not exceed 50 degrees Centigrade 
(122 degrees Fahrenheit). 

2. When heated to normal full load operating tem- 

perature, the insulation of transformers shall with- 
stand continuously for one minute a difference of 
•potential (alternating) between primary and sec- 
ondary coils and between the primary coils and 
the core according to the following table: — 
Primary or Secondary 

Voltage. Test Voltage. 

Not exceding 400 volts 1,500 

From 400 to 550 volts 2,000 

Over 550 volts.... To follow the standardization 
rules of the American Insti- 
tute of Electrical Engineers. 

82. Lightning Arresters. 

(For installation rules, see No. 3.) 

a. Lightning arresters must be of approved construction. 
(wSee list of Electrical Fittings.) 

83, Electric Signs (for Low-Potential Systems only). 

(For installation rules, see No. 23 d.) 

a. Material. 

Must be constructed entirely of metal or other approved 
non-combustible material except that wood may be used on 
outside for decoration if kept at least two inches from near- 
est lamp receptacles. 



FITTINGS, MATERIALS, ETC. 373 

Sheet metal must be not less than No. 28 U. S. metal gage. 

All metal must be galvanized, enameled or treated with 
at least three coats of anti-corrosive paint, or otherwise pro- 
tected in an approved manner against corrosion. 

b. Construction. 

Must be so constructed as to secure ample strength and 
rigidity. 

Must be so constructed as to be practically weatherproof 
and so as to enclose all terminals and wiring other than the 
supply leads, except that open work will be permitted for 
signs on roofs or open ground where not subject to me- 
chanical injury, provided the wiring is in accordance with 
Section "e" below. 

Cut-outs, transformers, unless of weatherproof type, flash- 
ers and other similar devices on or within the sign structure, 
must be in a separate, completely enclosed, accessible and 
weatherproof compartment, or, in a substantial weatherproof 
box or cabinet of metal of thickness not less than that of 
the metal of the sign itself. 

Each compartment must have suitable provision for drain- 
age through one or more holes each not less than one-quar- 
ter inch in diameter. 

c. Marking. 

Must have the maker's name or trademark permanently 
attached to the exterior. 

d. Receptacles. 

Must be so designed as to afford permanent and reliable 
means to prevent possible turning; must be so designed and 
placed that terminals will be at least one-half inch from 
other terminals and from metal of the sign except that where 
open work is permitted, this separation must be one inch. 

Miniature receptacles will not be approved for use in 
outdoor signs. 

e. Wiring. 

Must be approved rubber covered, not less than No. 14 
B. and S. gage, and, except where open work is permitted, 
must be double braided. 



374 MODERN ELECTRICAL CONSTRUCTION. 

Must be neatly run, and so disposed and fastened as to be 
mechanically secure. 

Must be soldered to terminals, and exposed parts of wires 
and terminals must be treated to prevent corrosion. 

Must, where they pass through walls or partitions of the 
sign, be protected by approved bushings. 

On outside of sign structure, except where open work is 
permitted, must be in approved metal conduit or in approved 
armored cable. 

For open work, wire must be rigidly supported on non- 
combustible, non-absorptive insulators, which separate the 
wires at least one inch from the surface wired over. Rigid 
supporting requires, under ordinary conditions where wiring 
over flat surfaces, supports at least every four and one-half 
feet. If the wires are liable to be disturbed, the distances be- 
tween supports should be shortened. In those parts of cir- 
cuits where wires are connected to approved receptacles which 
hold them at least one inch from surface wired over, and 
which are placed not uver one foot apart, such receptacles 
will be considered to afford the necessary support and spac- 
ing of the wires. Between receptacles more than one foot, 
but less than two feet apart, an additional non-combustible, 
non-absorptive insulator maintaining a separation and spac- 
ing equivalent to the receptacles must be used. Except as 
above specified, wires must be kept apart at least two and one- 
half inches for voltages up to 300, and four inches for higher 
voltages. 

f. Leads from sign must pass through the walls of sign 
either through approved metal conduit or armored cable, or 
must be neatly cabled and pass through one or more approved 
non-combustible, non-absorptive bushings. 

g. Not over 1,320 watts shall be dependent upon final cut- 
out. 



SIGN HANGING. 

The N. E. Code recognizes none but signs made entirely of 
meta\ nevertheless there are at the present time many signs 
of wood construction installed and in Figure 203 such a sign 
is shown. In the hanging of these old wooden signs certain 



FITTINGS, MATERIALS, ETC. 







376 



MODERN ELECTRICAL CONSTRUCTION. 



precautions are necessary that are not called for in connection 
with metallic signs. The framework of a wood sign is gen- 
erally made up as indicated in Figure 204 and where the 




Figure 204. 



top and side pieces come together the wood soon begins to 
decay sufficiently to weaken the structure. For this reason 
the cross pieces on the supporting bolts should be long 
enough to catch the outside boards of sign as these carry the 



FITTINGS, MATERIALS, ETC. $77 

letters and make up nearly the whole weight of the sign. The 
manner of supporting the rear end of sign is also open to 
serious objections and if the sign is at all heavy it is ad- 
visable to provide an extra bolt at rear and attach this to an 
extra cable as shown by broken lines, Figure 203. 

If signs are required to swing as they are in many cities 
it will be necessary to arrange the turning points at top end 
of cable to be perpendicularly above the turning points at 
sign otherwise the sign will not swing level. 

Wherever possible signs should be supported by bolts 
passing through brick or stone walls. The fronts of such 
walls are not always of the best and usually consist of ve- 
neering which is merely stuck on and quite flimsy. 

In Figure 205 is shown the cross-section of an expansion 
bolt which has shown itself to be very serviceable. It is made 
of the shape shown, the black portion representing a lead 
sleeve which surrounds the bolt. After the bolt is in 
place the lead is pounded in with a small piece of pipe. The 
lead thus forced in expands into every crevice in the drill 
hole thus, not only holding the bolt very tight, but also ex- 
cluding all water that might cause corrosion or decay. If 
the brick or stone itself is secure this form of support is very 
substantial. 

The supports to a sign should always be arranged as high 
above the sign as possible if dependence is to be placed upon 
expansion belts. At low angles the pull is almost straight 
out from the wall while at a high elevation the pull is 
downward. 

The side strain on side guys in a storm is much greater 
than the weight of the sign imposes upon them in support but 
of course a side guy giving way, if the sign is arranged to 



378 MODERN ELECTRICAL CONSTRUCTION. 

swing, does not necessarily allow the sign to fall. The wind 
pressure in heavy storms and at velocities often met with in 
narrow streets is 30 pounds or more per square foot. This 
for a sign 10 by 3 feet equals 900 pounds, while a sign of this 
size would not ordinarily weigh above 300. 

The side guys should be spread at least at an angle of 45 
degrees and where this is not possible stiff braces should 
preferably be used on both sides. If such guys are tight there 
will not only be a pull against the wind but a push also. 

Wherever the cables are attached to sign they should be 
protected by sleeves and clamped together by two clips as 



Y///S/SS,7SS/S//////////ft 




^/'/////////WM^ 



Figure 205. 

shown in the figure. Good galvanized cable should be used. 
A poor cable in the center of a large city will show strong 
evidence of rusting in less than a year, while a good one 
will last a very long time. In the outskirts the effect of rust 
is less marked and most any galvanized cable will last sev- 
eral years. 

It is good practice to remove any cable that shows the 
slightest evidence of rusting. In the early days of electric 
sign hanging quite frequently old elevator cables were used 
for that purpose. Several of these rusted fast enough to 
part in less than a year. 



FITTINGS, MATERIALS, ETC. 379 

84. 

Left blank for future use. 



Class E. 
MISCELLANEOUS. 

85. Signaling Systems. 

Governing wiring for telephone, telegraph (except wire- 
less telegraph apparatus) , district messenger and call-bell cir- 
cuits, fire and burglar alarms, and all similar systems which 
are hazardous only because of their liability to become crossed 
with electric light, heat or power circuits. 

a. Outside wires should be run in underground ducts or 
strung on poles, and kept off of the roofs of buildings, except 
by special permission of the Inspection Department having 
jurisdiction, and must not be placed on the same cross-arm 
with electric light or power wires. They should not occupy 
the same duct, manhole or handhole of conduit systems with 
electric light or power wires. 

Single manholes, or handholes separated into sections by 
means of partitions of brick or tile will be considered as con- 
forming with the above rule. 

The liability of accidental crossing of overhead signaling cir- 
cuits with electric light and power circuits, may be guarded against 
to a considerable extent by endeavoring to keep the two classes of 
circuits on different sides of the same street. 

When the entire circuit from Central Station to building 

is run in underground conduits, Sections b to m 

inclusive do not apply. 

b. When outside wires are run on same pole with electric 
light or power wires, the distance between the two inside pins 
of each cross-arm must not be less than twenty-four inches. 

Signaling wires being smaller and more liable to break and fall, 
should generally be placed on the lower cross-arms. 

When the wires are carried in approved cables, the next 
three sections (c, d and e) do not apply. 

c. Where wires are attached to the outside walls of build- 
ings, they must have an approved rubber insulating covering, 



MISCELLANEOUS. 38 1 

and on frame buildings or frame portions of other buildings 
shall be supported on glass or porcelain insulators, or knobs. 

d. The wires from last outside support to the cut-outs 
or protectors must be of copper, and must have an approved 
rubber insulation. Must be provided with drip loops im- 
mediately outside the building and at entrance. 

e. Wires must enter building through approved non- 
combustible, non-absorptive, insulating bushings sloping up- 
ward from the outside. 

Installations zvhere the Current-carrying Parts of the Ap- 
paratus Installed are Capable of Carrying Indefinitely 
a Current of Ten Amperes. 

f. An all-metallic circuit shall be provided, except in 
telegraph systems. 

g. At the entrance of wires to building, approved single 
pole cut-outs, designed for 251-600 volts potential and con- 
taining fuses rated at not over ten amperes capacity, shall 
be provided for each wire. These cut-outs must not be 
placed in the immediate vicinity of easily ignitible stuff, or 
where exposed to inflammable gases, or dust or to flying of 
combustible material. 

h. The wires inside building shall be of copper not less 
than No. 16, B. & S. gage, and must have insulation and be 
supported, the same as would be required for an installation 
of electric light or power wiring, 0-600 volts potential. 

i. The instruments shall be mounted on bases constructed 
of non-combustible, non-absorptive, insulating material. Holes 
for the supporting screws must be so located or countersunk, 
that there will be at least one-half inch space, measured over 
the surface, between the head of the screw and the nearest 
live metal part. 

Installations where the Current-carrying Parts of the Ap- 
paratus Installed are Not Capable of Carrying In- 
definitely a Current of Ten Amperes. 

j. Must be provided with an approved protective device 
located as near as possible to the entrance of wires to build- 
ing. The protector must not be placed in the immediate 
vicinity of easily ignitible stuff, or where exposed to inflam- 
mable gases or dust or flyings of combustible materials. 



382 MODERN ELECTRICAL CONSTRUCTION. 

k. Wires from entrance to building to protector must be 
supported on porcelain insulators, so that they will come in 
contact with nothing except their designed supports. 

/. The ground wire of the protective device shall be run 
in accordance with the following requirements : — 

1. Shall be of copper and not smaller than No. 18 B. 

& S, gage. 

2. Must have an insulating covering approved for volt- 

ages from o to 600, except that the preservative 
compound may be omitted. 

3. Must run in as straight a line as possible to a good 

permanent ground. This may be obtained by con- 
necting to a water or gas pipe connected to the 
street mains or to a ground rod or pipe driven 
in permanently damp earth. When connections are 
made to pipes, preference shall be given to water 
pipes. If attachment is made to gas pipe, the 
connection in all cases must be made between the 
meter and the street mains. In every case the 
connection shall be made as near as possible to 
the earth. 

When the ground wire is attached to a water pipe 
or a gas pipe, it may be connected by means of 
an approved ground clamp fastened to a thor- 
oughly clean portion of said pipe, or the pipe 
shall be thoroughly cleaned and tinned with rosin 
flux solder, and the ground wire shall then be 
wrapped tightly around the pipe and thoroughly 
soldered to it. 

When the ground wire is attached to a ground rod 
driven into the earth, the ground wire shall be 
soldered to the rod in a similar manner. 

Steam or hot-water pipes must not be used for a pro- 
tector ground. 

m. The protector to be approved must comply with the 
following requirements : — 

For Instrument Circuits of Telegraph Systems. 

1. An approved single pole cut-out, in each wire, de- 
signed for 2,000 volts potential, and containing 



MISCELLANEOUS. 383 

fuses rated at not over one ampere capacity. 
When main line cut-outs are installed as called 
for in section g, the instrument cut-outs may be 
placed between the switchboard and the instru- 
ment as near the switchboard as possible. 

For all Other Systems. 

1. Must be mounted on non-combustible, non-ab- 

sorptive, insulating bases, so designed that when 
the protector is in place, all parts which may be 
alive will be thoroughly insulated from the wall 
to which the protector is attached. 

2. Must have the following parts : — 

A lightning arrester which will operate with a diffeience 
of potential between wires of not over 500 volts, 
and so arranged that the chance of accidental 
grounding is reduced to a minimum. 

A fuse designed to open the circuit in case the wire 
become crossed with light or power circuits. The 
fuse must be able to open the circuit without 
arcing or serious flashing when crossed with any 
ordinary commercial light or power circuit. 

A heat coil, if the sensitiveness of the instrument de- 
mands it, which will operate before a sneak cur- 
rent can damage the nstrument the protector is 
guarding. 

Heat coils are necessary in all circuits normally closed 
through magnet windings, which cannot indefi- 
nitely carry a current of at least five amperes. 

The heat coil is designed to warm up and melt out with a 
current large enough to endanger the instruments if con- 
tinued for a long time, but so small that it would not 
blow the fuses ordinarily found necessary for such in- 
struments. The smaller currents are often called "sneak" 
currents. 

3. The fuses must be so placed as to protect the ar- 

rester and heat coils, and the, protector terminals 
must be plainly marked "line/' "instrument," 
"ground." 
An easily read abbreviation of the above words will be 
allowed. 



384 MODERN ELECTRICAL CONSTRUCTION. 

The Following Rules Apply to All Systems whether the 

Wires from the Central Office to the Building are 

Overhead or Underground. 

n. Wires beyond the protector, or wires inside buildings 
where no protector is used, must be neatly arranged and se- 
curely fastened in place in some convenient, workmanlike 
manner. 

They must not come nearer than two inches to any elec- 
tric light or power wire in the building, unless separated there- 
from by some continuous and firmly fixed non-conductor creat- 
ing a permanent separation ; this non-conductor to be in addi- 
tion to the regular insulation on the wire. 

The wires would ordinarily be insulated, but the kind of insula- 
tion is not specified, as the protector is relied upon to stop all 
dangerous currents. Porcelain tubing or approved flexible tubing 
may be used for encasing wires where required as above. 

0. Wires where bunched together in a vertical run within 
any building must have a lire-resisting covering sufficient to 
prevent the wires from carrying fire from floor to floor unless 
they are run either in non-combustible tubing or in a fire- 
proof shaft, which shaft must be provided with fire stops at 
each floor. 

Signaling wires and electric light or power wires may be 
run in the same shaft, provided that one of these classes of 
wires is run in non-combustible tubing, or provided that when 
run otherwise these two classes of wires shall be separated 
from each other b}^ at least two inches. 

In no case shall signaling wires be run in the same tube 
with electric light or power wires. 

p. Transformers or other devices for supplying current 
to signaling systems from light, heat or power circuits must 
be of a design expressly approved for this purpose. The 
primary wiring must be installed in accordance with the rules 
for "Class C," and the secondarv wiring in accordance with 
"Class E." 

86. Wireless Telegraph Apparatus. 

Note. — Thesp rules do not apply to Wireless Telegraph apparatus 
installed on shipboard. 

In setting up Wireless Telegraph apparatus (so-called) 
all wiring within the building must conform to the Rules and 



MISCELLANEOUS. 385 

Requirements of the National Electrical Code for the class 
of work installed and the following additional specifications : — 

a. Aerial conductors to be permanently and effectively 
grounded at all times when station is not in operation by a 
conductor not smaller than No. 4 B. & S. gage copper wire, 
run in a direct line as possible to water pipe at a point on 
the street side of all connections to said water pipe within the 
premises, or to some other equally satisfactory earth con- 
nection. 

b. Aerial conductors when grounded as above specified 
must be effectually cut off from all apparatus within the build- 
ing. 

c. Or the aerial to be permanently connected at all times 
to earth in the manner specified above, through a short-gap 
lightning arrester ; said arrester to have a gap of not over 
.015 inch between brass or copper plates not less than 2 l /> 
inches in length parallel to the gap and i l /2 inches the other 
way with a thickness of not less than one-eighth inch mounted 
upon non-combustible, non-absorptive, insulating material of 
such dimensions as to give ample strength. Other approved 
arresters of equally low resistance and equally substantial 
construction may be used. 

d. In cases where the aerial is grounded as specified in 
paragraph 1, the switch employed to join the aerial to the 
ground connection shall not be smaller than a standard ioo 
ampere knife switch. 

e. Where supply is obtained direct from the street service 
the circuit must be installed in approved metal conduits or 
armored cable. In order to protect the supply system from 
high potential surges, there must be inserted in circuit either 
a transformer having a ratio which will have a potential on 
the secondary leads not to exceed 550 volts, or two condensers 
in series across the line, the connection between said con- 
densers to be permanently and effectually grounded. These 
condensers should have capacity of not less than one-half m. f. 

87. Electric Gas Lighting. 

a. Electric gas lighting, unless it is the frictional system. 
must not be used on the same fixture with the electric light. 

88. Insulation Resistance. 

The wiring in any building must test free from grounds ; 



•386 MODERN ELECTRICAL CONSTRUCTION. 

i. e. } the complete installation must have an insulation be- 
tween conductors and between all conductors and the ground 
(not including attachments, sockets, receptacles, etc.) not less 
than that given in the following table : — 

Up to 5 amperes 4,000,000 ohms. 

Up to 10 amperes 2,000,000 ohms. 

Up to 25 amperes 800,000 ohms. 

Up to 50 amperes 400,000 ohms. 

Up to 100 amperes 200,000 ohms. 

Up to 200 amperes 100,000 ohms. 

Up to 400 amperes 50,000 ohms. 

Up to 800 amperes 25,000 ohms. 

Up to 1,600 amperes 12,500 ohms. 

The test must be made with all cut-outs and safety devices 
in place. If the lamp sockets, receptacles, electroliers, etc., 
are also connected, only one-half of the resistances specified 
in the table will be required. 

89. Soldering Fluid. 

a. The following formula for soldering fluid is sug 
gested : — 

Saturated solution of zinc chloride 5 parts 

Alcohol 4 parts 

Glycerine 1 part 



Class F. 
MARINE WORK. 



90. Generators. 



a. Must be located in a dry place. 

b. Must have their frames insulated from their bed-plates. 

c. Must each be provided with a waterproof cover. 

d. Must each be provided with a name-plate, giving the 
maker's name, the capacity in volts and amperes, and the nor- 
mal speed in revolutions per minute. 

91. Wires. 

a. Must be supported in approved moulding or conduit, 
except at switchboards and for portables. 

Special permission may be given for deviation from this rule 
in dynamo-rooms. 

b. Must have no single wire larger than No. 12 B. & S. 
gage. Wires to be stranded when greater carrying capacity 
is required. No single solid wire smaller than No. 14 B. & 
S. gage, except in fixture wiring to be used. 

Stranded wires must be soldered before being fastened un- 
der clamps or binding screws, and when they have con- 
ductivity greater than that of No. 8 B. & S. gage copper wire 
they must be soldered into lugs. 

c. Splices or taps in conductors must be avoided as far 
as possible. Where it is necessary to make them they must 
be so spliced or joined as to be both mechanically and electric- 
ally secure without solder. They must then be soldered, to 
insure preservation, covered with an insulating compound 
equal to the insulation of the wire, and further protected by a 
waterproof tape. The joint must then be coated or painted 
with a waterproof compound. 

All joints must be soldered unless made with some form of 
approved splicing device. 



388 MODERN ELECTRICAL CONSTRUCTION. 

For Moulding Work. 

d. Must have an approved insulating covering at least 
three thirty-seconds of an inch in thickness and be covered 
with a substantial waterproof braid. 

The physical characteristics shall not be affected by any 
change in temperature up to 200 degrees Fahrenheit (93 de- 
grees Centigrade). After two weeks' submersion in salt water 
at 70 degrees Fahrenheit (21 degrees Centigrade), it must 
show an insulation resistance of 100 megohms per mile after 
three minutes' electrification with 550 volts. 

e. Must have, when passing through water-tight bulk- 
heads and through all decks, a metallic stuffing tube lined with 
hard rubber. In case of deck tubes, they must be boxed near 
deck to prevent mechanical injury. 

/. Must be bushed with hard rubber tubing, one-eighth 
of an inch in thickness, when passing through beams and non- 
water-tight bulkheads. 

For Conduit Work. 

g. Must have an approved insulating covering. 

The insulation for conductors, for use in lined conduits, 
to be approved, must be at least three thirty-seconds of an 
inch in thickness and be covered with a substantial water- 
proof braid. The physical characteristics shall not be affected 
by any change in temperature up to 200 degrees Fahrenheit 
(93 degrees Centigrade). 

After two weeks' submersion in salt water at 70 degrees 
Fahrenheit (21 degrees Centigrade), it must show an in- 
sulation resistance of 100 megohms per mile after three min- 
utes' electrification with 550 volts. 

For unlined metal conduits, conductors must conform to 
the specifications given for lined conduits, and in addition 
have a second outer fibrous covering at least one thirty-sec- 
ond of an inch in thickness and sufficiently tenacious to 
withstand the abrasion of being hauled through the metal 
conduit. 

h. Must not be drawn in until the mechanical work on 
the conduit is completed and same is in place. 



MARINE WORK. 3§9 

I. Where run through coal bunkers, boiler rooms, and 
where they are exposed to severe mechanical injury, must be 
encased in approved conduit. 

/. Must, for alternating systems, have the two or more 
wires of a circuit drawn in the same conduit. 

The same conduit must not contain more than four two- 
wire, or three three-wire circuits of the same system, except 
by special permission of the Inspection Department having 
jurisdiction, and must never contain circuits of different sys- 
tems. 

It is suggested that this be done for direct current systems also, 
^o that they may be changed to alternating systems at any time, 
induction troubles preventing such a change if the wires are in 
separate conduits. 

92. Portable Conductors. 

a. Must be made of two stranded conductors each hav- 
ing a carrying capacity equivalent to not less than No. 14 B. 
and S. gage, and each covered with an approved insulation and 
covering. 

Where not exposed to moisture or severe mechanical in- 
jury, each stranded conductor must have a solid insulation at 
least one thirty-second of an inch in thickness, and must 
show an insulation resistance between conductors, and between 
either conductor and the ground, of at least fifty megohms 
per mile after two weeks' submersion in water at 70 degrees 
Fahrenheit (21 degrees Centigrade), and be protected by a 
slow-burning, tough-braided outer-covering. 

Where exposed to moisture and mechanical injury (as for 
use on decks, holds and fire-rooms) each stranded conductor 
shall have a solid insulation, to be approved, of at least one 
thirty-second of an inch in thickness and protected by a tough 
braid. The two conductors shall then- be stranded together, 
using a jute filling. The whole shall then be covered with 
a layer of flax, either woven or braided, at least one thirty- 
second of an inch in thickness and treated with a non-in- 
flammable, waterproof compound. After one week's submer- 
sion in water at 70 degrees Fahrenheit (21 d^rees Centi- 
grade), it must show an insulation between the two con- 
ductors, or between either conductor and the ground, of fifty 
megohms per mile. 



390 



MODERN ELECTRICAL CONSTRUCTION. 



93. Bell or Other Wires. 

a. Must never be run in same duct with lighting or power 
wires. 

94. Table of Allowable Capacity of Wires. 



Amperes. 



6 

'i2 

17 
21 

25 

30 

35 

40 

50 

60 

70 

85 

100 

120 

145 

170 

200 

235 

270 

320 

340 

When greater conducting area than that of 12 B. & S. gage 
is required, the conductor shall be stranded in a series of 7, 
l 9, 37, 61, 91 or 127 wires, as may be required ; the strand con- 
sisting of one central wire, the remainder laid around it con- 
centrically, each layer to be twisted in the opposite direction 
from the preceding. 

95. Switchboard. 

a. Must be made of non-combustible, non-absorptive, in- 
sulating material, such as marble or slate. 

b. Must be kept free from moisture, and must be located 
so as to be accessible from all sides. 

c. Must have a main switch, main cut-out and ammeter 
for each generator. 





Area 




Size of 




Actual N 


0. of 


Strands 


B. & S. G. 


B. & S. G 


] 


L9 1,288 




# # 


18 1,624 


. . 


# # 


] 


L7 2,048 


. . 


. . 


16 2,583 


, . 


# # 


15 3,257 


. . 


# # 


] 


L4 4,107 


. . 


. . 


] 


L2 6,530 


, . 


, . 




9,016 


7 


19 




11,368 


7 


18 




14,336 


7 


17 




. . • 18,081 


7 


16 




22,799 


7 


15 




30,856 


19 


18 




38,912 


19 


17 




49,077 


19 


16 




60,088 


37 


18 




75,776 


37 


17 




99,064 


61 


18 




124,928 


61 


17 




157,563 


61 


16 




198,677 


61 


15 




250,527 


61 


14 




296,387 


91 


15 




373,737 


91 


14 




413,639 : 


L27 


15 



MARINE WORK. 391 

Must also have a voltmeter and ground detector. 

d. Must have a cut-out and switch for each side of each 
circuit leading from the board. 

e. Must be wired with conductors having an insulation as 
required for moulding or conduit work and covered with a 
substantial flameproof braid. 

96. Resistance Boxes. 

(For construction rules, see No. 78.) 

a. Must be located on switchboard or away from cum- 
bustible material. When not placed on switchboard they must 
be mounted on non-inflammable, non-absorptive, insulating 
material. 

97. Switches. 

(For construction rules, see No. 65.) 

a. When exposed to dampness, they must be enclosed in 
a water-tight case. 

b. Must be of the knife pattern when located on switch- 
board. 

c. Must be provided so that each freight compartment 
may be separately controlled. 

98. Cut-Outs. 

(For construction rules, see No. 67.) 

a. Must be placed at every point where a change is made 
in the size of the wire (unless the cut-out in the larger wire 
will protect the smaller). 

b. In such places as upper decks, holds, cargo spaces and 
fire-rooms, a water-tight and fireproof cut-out may be used, 
connecting directly to mains when such cut-out supplies cir- 
cuits requiring not more than 660 watts energy. 

c. When placed anywhere except on switchboards must 
be enclosed in a cabinet lined with fire-resisting material. 

d. Except for motors, searchlights and diving lamps must 
be so placed that no group of lamps, requiring a current of 
more than 660 watts, shall ultimately be dependent upon one 
cut-out. 



392 MODERN ELECTRICAL CONSTRUCTION. 

99. Fixtures. 

a. Must be mounted on blocks made from well-seasoned 
lumber treated with two coats of white paint or shellac. 

b. Where exposed to dampness, the lamp must be sur- 
rounded by a vapor-proof globe. 

c. Where exposed to mechanical injury, the lamp must be 
surrounded by. a globe protected by a stout wire guard. 

d. Must be wired with same grade of insulation as port- 
able conductors which are not exposed to moisture or mechan- 
ical injury. 

e. Ceiling fixtures over two feet in length must be pro* 
vided with stay chains. 

100. Sockets. 

(For construction rules, see Xo. 72.) 

101. Wooden Mouldings. 

(For construction rules, see No. 60.) 

a. Where moulding is run over rivets, beams, etc., a back- 
ing strip must first be put up and the moulding secured to this.. 

b. Capping must be secured by brass screws. 

102. Interior Conduits. 

(For construction rales, see A T o. 58.) 

a. No conduit tube having an internal diameter of less 
than five-eighths of an inch shall be used. Measurements to 
be taken inside of metal conduits. 

b. Must be continuous from outlet to outlet or to junc- 
tion boxes, and the conduit must properly enter and be se- 
cured to all fittings, and the entire system must be mechan- 
ically secured in position. 

, In case of main runs, this involves running each conduit 
continuously into a main cut-out cabinet or gutter surround- 
ing the panel board, as the case may be. 

. • c. Must be first installed as a complete conduit system, 
without the conductors. 

d. Must be equipped at every outlet with an approved out- 
let box or plate. 



MARINE WORK. 393 

Outlet plates must not be used where it is practicable to 
install outlet boxes. 

The outlet box or plate must be so installed that it will 
be flush with the finished surface, and if this surface is 
broken it shall be repaired so that it will not show any gaps 
or open spaces around the edge of the outlet box or plate. 

In vessels already constructed where the conditions are 
such that neither outlet box nor plate can be installed, these 
appliances may be omitted by special permission of the In- 
spection Department having jurisdiction, providing the con- 
duit ends are bushed and secured. 

It is suggested that outlet boxes and fittings having conductive 
coatings be used in order to secure better electrical contact at all 
points throughout the conduit system. 

e. Metal conduits where they enter junction boxes, and 
at all other outlets, etc., must be provided with approved 
bushings fitted so as to protect wire from abrasion, except 
when such protection is obtained by the use of approved 
nipples, properly fitted in boxes or devices. 

f. Must have the metal of the conduit permanently and 
effectually grounded. 

Conduits must be securely fastened in metal outlet boxes 
so as to secure good electrical connection. If conduit, coup- 
lings, outlet boxes or fittings having protective coating of non- 
conducting material, such as enamel, are used, such coating 
must be thoroughly removed from threads of both couplings 
and conduit and from surfaces of boxes and fittings where the 
conduit is secured in order to obtain the requisite good con- 
nection. Where boxes used for centers of distribution do not 
afford good electrical connection, the conduits must be bound 
around them by suitable bond wires. Where sections of metal 
conduit are installed without being fastened to the metal struc- 
ture of vessels or grounded metal piping, they must be 
bonded together and joined to a permanent and efficient 
ground connection. • 

Connections to grounded pipes and to conduit must be ex- 
posed to view or readily accessible, and must be made by 
means of approved ground clamps to which the ground wires 
must be soldered. 

Ground wires must be of copper, at least No. 10 B. & S. 
gage (where largest wire contained in conduit is not greater 



394 MODERN ELECTRICAL CONSTRUCTION. 

than No. o B. & S. gage), and need not be greater than No. 
4 B. & S. gage (where largest wire contained in conduit is 
greater than No. o B. & S. gage). They shall be protected 
from mechanical injury. 

g. Junction boxes must always be installed in such a 
manner as to be accessible. 

h. All elbows or bends must be so made that the conduit 
or lining of same will not be injured. The radius of the curve 
of the inner edge of any elbow not to be less than three and 
one-half inches. Must have not more than the equivalent of 
four-quarter bends from outlet to outlet, the bends at the out- 
lets not being counted. 

103. Signal Lights. 

a. Must be provided with approved telltale board, located 
preferably in pilot house, which will immediately indicate a 
burned-out lamp. 

104. Motors. 

a. Must be wired under the same precautions as with a 
current of same volume and potential for lighting. The motor 
and resistance box must be protected by a double-pole cut-out 
and controlled by a double-pole switch, except in cases where 
one-quarter horse power or less is used. 

The motor leads or branch circuits must be designed to 
carry a current at least 25 per cent greater than that for 
which the motor is rated. Where the wires under this rule 
would be overfused, in order to provide for the starting cur- 
rent, as in the case of many of the alternating current, motors, 
the wires must be of such size as to be properly protected by 
these larger fuses. 

b. Must be thoroughly insulated. Where possible, should 
be set on base frames made from filled, hard, dry wood and 
raised above surrounding deck. On hoists and winches they 
must be insulated from bed-plates by hard rubber, fiber or 
similar insulating material. 

c. Must be covered with a waterproof cover when not in 
use. 

d. Must each be provided with a name-plate giving maker's 
name, the capacity in volts and amperes, and the normal 
speed in revolutions per minute. 



MARINE WORK. 395 

105. Insulation Resistance. 

The wiring in any vessel must test free from grounds ; L e., 
the complete installation must have an insulation between con- 
ductors and between all conductors and the ground (not in- 
cluding attachments, sockets, receptacles, etc.), of not less than 
the following: — 

Up to 25 amperes 800,000 ohms. 

Up to 50 amperes 400,000 ohms. 

Up to 100 amperes 200,000 ohms. 

Up to 200 amperes 100,000 ohms. 

Up to 400 amperes 50,000 ohms. 

Up to 800 amperes 25,000 ohms. 

Up to 1,600 amperes 12,500 omhs. 

All cut-outs and safety devices in place in the above. 
Where lamp sockets, receptacles and electroliers, etc., are 
connected, one-half of the above will be required. 



USEFUL INFORMATION. 



RESUSCITATION FROM ELECTRIC SHOCK. 
Rules Recommended by 

COMMISSION ON RESUSCITATION FROM 
ELECTRIC SHOCK 

Representing 

The American Medical Association 

The National Electric Light Association 

The American Institute of Electrical Engineers 

Dr. W. B. Cannon, Chairman; Professor of Physiology, 
Harvard University. 

Dr. Yandell Henderson, Professor of Physiology, Yale Uni- 
versity. 

Dr. S. J. Meltzer, Head of Department of Physiology and 
Pharmacology, Rockefeller Institute for Medical Research. 

Dr. Edw. Anthony Spitzka, Director and Professor of General 
Anatomy, Daniel Baugh Institute of Anatomy, Jefferson 
Medical College. 

Dr. George W. Crile, Professor of Surgery, Western Reserve 
University. 

W. C. L. Eglin, Past-President National Electric Light Asso- 
ciation. 

Dr. A. E. Kennelly, Professor of Electrical Engineering, Har- 
vard University. 

Dr. Elihu Thomson, Electrician, General Electric Company. 

W. D. Weaver, Secretary; Editor Electrical World. 

Issued and Copyrighted by 

NATIONAL ELECTRIC LIGHT ASSOCIATION 

Reprinted by Permission. 

Follow These Instructions Even if Victim Appears Dead. 

I. IMMEDIATELY BREAK THE CIRCUIT. 

With a single quick motion, free the victim from the cur- 
rent. Use any dry non-conductor (clothing, rope, board) to 



USEFUL INFORMATION. 



397 




O 






39^ MODERN ELECTRICAL CONSTRUCTION. 

move either the victim or the wire. Beware of using metal 
or any moist material. While freeing the victim from the 
live conductor have every effort also made to shut off the 
current quickly. 



II. INSTANTLY ATTEND TO THE VICTIM'S 
BREATHING. 

I. As soon as the victim is clear of the conductor, rapidly 
feel with your finger in his mouth and throat and remove any 
foreign body (tobacco, false teeth, etc.) Then begin artificial 
respiration at once. Do not stop to loosen the victim's clothing 
now ; every moment of delay is serious. Proceed as follows : 

a. Lay the subject on his belly, with arms extended as 
straightforward as possible and with face to one side, so that 
nose and mouth are free for breathing (see Fig. 206). Let 
an assistant draw forward the subject's tongue. 

b. Kneel straddling the subject's thighs and facing his 
head; rest the palms of your hands on the loins (on the 
muscles of the small of the back), with fingers spread over the 
lowest ribs, as in Fig. 206. 

c. With arms held straight, swing forward slowly so that 
the weight of your body is gradually, but not violently, brought 
to bear upon the subject (see Fig. 207). This act should take 
from two to three seconds. 

Immediately swing backward so as to remove the pressure, 
thus returning to the position shown in Fig. 206. 

d. Repeat deliberately twelve to fifteen times a minute the 
swinging forward and back — a complete respiration in four or 
five seconds. 

e. As soon as this artificial respiration has been started, 
and while it is being continued, an assistant should loosen 
any tight clothing about the subject's neck, chest or waist. 



USEFUL INFORMATION. 



399 




400 MODERN ELECTRICAL CONSTRUCTION. 

2. Continue the artificial respiration (if necessary, at least 
an hour), without interruption, until natural breathing is re- 
stored, or until a physician arrives. If natural breathing stops 
after being restored, use artificial respiration again. 

3. Do not give any liquid by mouth until the subject is 
fully conscious. 

4. Give the subject fresh air, but keep him warm. 

III. SEND FOR NEAREST DOCTOR AS SOON 
AS ACCIDENT IS DISCOVERED. 

PRACTICAL HINTS. 

A full description of the Wheatsone bridge, the telephone, 
magneto and other instruments, as well as the many ways of 
their application in testing for defects and for circuits in elec- 
trical installations having been given in a previous work of the 
authors (Wiring Diagrams and Descriptions) it is not thought 
necessary to repeat them here, especially as a work of this 
kind is necessarily limited in diagrams which would be re- 
quired to a full understanding of methods. This chapter will, 
therefore, consist only of such hints and instructions as apply 
to general work. 

An electric light circuit may be tested for "short circuit" by 
connecting an incandescent lamp in place of one of the fuses. 
If the lamp burns while there are no lamps in circuit, there is 
sure to be a short circuit. A low candle-power lamp will indi- 
cate with less current than a high-candle-power lamp and is, 
therefore, better. If no lamp is available a small fuse should 
first be tried. 



USEFUL INFORMATION. 401 

A test for "ground" may be made in the same way, but the 
lamp must be connected to both sides in turn and the fuse left 
out. If the main system to which the circuit to be tested con- 
nects is not grounded, a temporary ground must be put on. 
This is best done by connecting a lamp with one wire to a gas 
or water pipe and the other to the "live" binding screw on the 
opposite side of cutout to that in which the other lamp is con- 
nected. Thus, in Figure 20&, if a ground should exist at 3 and 




oooooooOQ-gyfr 



Figure 208. 

the lamp be connected to gas pipe, as shown, the test lamp at 
1 would burn. 

If a voltmeter were connected in place of either of the 
lamps, the test would be much more searching. 

With 3-wire systems no ground need be put on, as the neu- 
tral wire will always be found grounded. The lamp need be 
tried in the outside fuses only. This test will be more search- 
ing if lamps are placed in all sockets connected. 

In placing fuses in the 3-wire, 110-220 volt system, the neu- 
tral wire should always be fused first. 

By reference to Figure 209 it will be seen that while the 
neutral fuse in main blocks a is out, the two circuits of lamps 
c and d must burn in series; that is, just as much current must 
pass through one circuit as through the other. So long as 
there is an equal number of lamps in each circuit there is no 
trouble ; but should most of the lamps in one circuit be turned 
off, those remaining would have to carry all the current that 
passes through the lamps of the other circuit. This current 



402 



MODERN ELECTRICAL CONSTRUCTION. 



would overheat them and break, or burn them out in a very 
short time. If the neutral fuse is in place, each circuit is inde- 
pendent of the other and the neutral wire only carries the 
difference in current between the two sets of lamps. In order 
to insure against a neutral fuse "blowing" first in case of 
trouble, it is generally made heavier than in the outside wires. 
When a 3-wire circuit is to be cut off, the outside fuses should 
be drawn first. 

In order to find which is the "neutral" wire, two no volt 
lamps are connected in series and the wires from them brought 
in contact with two of the three wires. If both lamps burn at 
full candle power we have 220 volts, which is the pressure of 
the outside wires, and, therefore, the other wire must be the 



c 3 5 5 [pffPoi ^6 6 6 6 6 6 6 6 g-g~g > 



W? 




Figure 209. 



neutral. If the lamps burn only at half candle power, we 
have only no volts and one of the wires must be the neutral. 
That wire which gives no volts with either one of the other 
two wires is the neutral; this wire should always be run in 
the center between the other two. 

A test for the neutral wire can also be made by connecting 
a lamp to ground. A lamp connected this way will burn from 
either of the outside wires, but not from the neutral. 

If the neutral wire should be connected to any but the 
middle binding post of 3-wire cutouts and the outside wire 
made. (See Section 1.) 



USEFUL INFORMATION. 403 

to the other two, one-half of the lamps would be almost im- 
mediately destroyed, being subject to 220 volts, while the 
other half would burn properly. 

If a short circuit occurs, say at e, Figure 209, on one side 
of a 3-wire system and blows the neutral fuse on that side of 
the circuit, we shall have 220 volts on the lamps on the oppo- 
site side. This will quickly burn them out. Most of these 
troubles are avoided to some extent by the use of such branch 
cutouts as shown. This confines trouble of this kind to the 
mains. 

On any system having a neutral wire or a wire on one side 
grounded, if a ground on either of the other wires occurs, the 
trouble can be temporarily remedied by simply changing the 
two wires of that circuit at the cutout. This will transfer 
the ground to the side already grounded, so that it will not 
interfere with operation. The ground must, however, be 
cleared up at once as no grounding is ever allowed inside of 
any building. 

When strip cutouts are set horizontally and there is no 
bridge between opposite polarities, there will be the possibility 
of a partially melted upper fuse sagging down and forming a 
short circuit. 

On panel boards where fuses are set too close together, the 
heat of one fuse while blowing will often blow the next fuse 
above it. 

If large fuses are enclosed in small and very tight cabi- 
nets, the vapors formed by blowing will often cause short 
circuits. 

Before installing fuses in a "loaded" circuit, it is advisable 
to disconnect as many lights and other devices as possible. If 
there is a main switch this can easily be done. If there is no 
such switch on that part of the system, the task of placing 
fuses is somewhat hazardous ; for at the very insta-nt that the 
second fuse touches its terminal a great rush of current will 



404 MODERN ELECTRICAL CONSTRUCTION. 

flow. If there happens to be a "short" on the line beth fuses 
will probably blow and may burn the operator's hands and 
face severely. In order to avoid this, extremely careful manip- 
ulation is necessary. The first fuse can be placed without 
any difficulty, as there will be no current flow unless the cir- 
cuits are grounded. Before attempting to place the second 
fuse the circuits may be tested for "shorts" by placing a 
"jumper" (a piece of wire heavy enough so that it will not 
be heated by the current it is to carry) with the ends on the 
other fuse terminals. This "jumper" will complete the cir- 
cuit and, if all is in order the lights will burn. If there are 
two men, one may hold the jumper while the other places the 
fuse, but it should be placed as quickly as possible, especially 
if the circuit has a motor load, for these will be started very 
soon after the lights come on and will greatly increase the 
current. If there is but one man the jumper may be tem- 
porarily fastened to the mains. 

A jumper is not absolutely necessary even with large fuses, 
for if the last contact is made quickly and held steady, there 
will be very little arcing; one should, however, provide all pro- 
tection possible. If a piece of asbestos is at hand, it may be 
used to cover the fuses, so as to protect the hands and face 
from melted metal. 

Before attempting to re-fuse a circuit, note condition of 
cutout block. If there is evidence of a great flash, it is very 
likely that the fuse was blown by a short circuit. If the 
blowing was caused by a slight overload or loose contact, the 
destructive eflect will be much less. 

Much trouble can be prevented by cleaning terminals of 
fuse blocks occasionally and going over nuts and screws to 
see that they are tight. 

In Figure 210, a shows the proper way of connecting small 
wires into such terminals. This method prevents the screw 
from cutting into the main wire and allowing it to break. 



USEFUL INFORMATION. 



405 



A wire should always be bent around the binding post of 
.switch or cutout in the direction in which the nut which is to 
hold it must turn to be fastened as in c. If a wire is not long 
enough to be bent around the post or screw, a small piece of 
wire should be placed opposite it so as to give a level bearing 
to nut or washer. See b. 

Plug cutouts having their metal parts projecting above the 
porcelain, as shown at d, should be connected, whenever pos- 





Figure 210. 

sible, so that these metal parts are dead when fuses are with- 
drawn. This will prevent many accidental short circuits. 

The positive and negative wires of a circuit can easily be 
determined by immersing both wires in a little water, keeping 
them an inch or so apart. Small bubbles will soon appear at 
the negative wire. 

If an arc lamp has been properly connected, the upper car- 
bon will be heated much more than the lower and will remain 
red longer. An arc lamp improperly connected is said to be 
burning "upside down" and will at once manifest itself by the 
strong light thrown against the ceiling. 

It is very often found necessary to determine the capacity 
of a cable which is already installed and where it is impossible 
to get at the separate wires of which it is formed. As cables 
are usually made up in a uniform manner, as shown in the 
table below, their capacity can be determined by the following 
method: To find the number of circular mils in a cable made 
up of wires of uniform size. Measure diameter of cable, 
count number of wires in outside layer, and, referring to the 



406 MODERN ELECTRICAL CONSTRUCTION. 

table below, find the same number in the first column ; divide 

the diameter of cable by the number set opposite this in the 

second column. This will give the diameter of each wire. 

Multiply this diameter by itself and then by the number of 

wires contained in cable as given in the third column. All 

measurements should be expressed in mils (1/1,000 inch) and 

the result will be the circular mils contained in cable. 

Outside layer 6 wires 3 times diameter 7 wires in cable 

Outside layer 12 wires 5 times diameter 19 wires in cable 

Outside layer 18 wires 7 times diameter 37 wires in cable 

Outside layer 24 wires 9 times diameter 61 wires in cable 

Outside layer 30 wires 11 times diameter 91 wires in cable 

Outside layer 36 wires 13 times diameter 127 wires in cable 

Outside layer 42 wires 15 times diameter 169 wires in cable 

The various figures in Figure 21 1 are designed to show how 
many single wires may be run in one conduit. Under each 
figure is given a number which, if multiplied by the diameter 
of the wire to be used will give the smallest diameter of 
tube which can contain the corresponding number of wires. 
Thus, for instance, if 12 wires are run through one tube or 
conduit, the diameter of that conduit must be at least 4 1/3 
times as great as the diameter of the wire to be used. Each 
figure illustrates the amount of spare room the correspond- 
ing number of wires leave, and it is necessary to use con- 
siderable judgment. Long runs will require more space, es- 
pecially if the wires be quite large. Much also expends upon 
the nature of the insulation and the temperature. The figures 
are believed to be correct for single wires and can be followed 
for twin wires, as the same number of conductors arranged 
that way will not occupy as much space as single wires. The 
actual diameter of lined and unlined conduits are given in an- 
other table and may be referred to. The best way to ac- 
curately determine the diameter of small wire consists in cut- 
ting a number of short pieces and laying them together, then 
measuring over all and dividing the measurement by the num- 
ber of wires. 



USEFUL INFORMATION. 



407 




Figure 211. 



408 MODERN ELECTRICAL CONSTRUCTION. 

TRICKS OF THE TRADE. 

Cases have been known where it was requested to replace 
single pole switches by double pole, that the single pole switch 
was replaced as requested, but, instead of running both wires 
through it as required, only one wire had been properly 
brought into it and the other two binding posts filled out with 
short pieces of wire calculated to deceive the inspector. A 
test to detect this without disconnecting the swtich is easily 
made. By reference to Figure 212 it will be seen that if a 
double pole snap switch is properly connected, current can 
be felt if the points a and b are touched with moistened fin- 
gers. If the switch is connected single pole, current can be 
felt at b and c, when the switch is open, only. 

On one occasion a wireman had run some wires on insu- 
lators along a ceiling and instead of soldering joints had care- 





Figure 212. Figure 213. 

fully, in many places above the joints, smoked the ceiling with 
a candle in order to deceive an inspector. 

In several cases where an "over-all" test of insulation re- 
sistance was made, meter loops which had been run in con- 
tinuous pieces were found with the wire "nicked" with a knife 
and then broken, leaving the insulation nearly intact, but the 



USEFUL INFORMATION. 4°9 

circuit open. A similar trick is often worked with the ground 
wire of ground detectors. 

In other cases plugs with fuses removed were put in 
"bad" circuits. In one case the real circuit wires (concealed 
work) were disconnected from cutouts and pushed back into 
the wall and short pieces connected instead. 

In another case where wire not up to requirements had 
been used and condemned, this wire, being run between joists 
and concealed by plastering, was pushed back and short 
pieces of approved wire stuck in at outlets. 

Sometimes in fished work after inspection the long pieces 
of loom reaching from outlet to outlet are withdrawn and 
short pieces at the outlets substituted. 

Lamp butts with wire terminals twisted together, or a 
strand of wire from lamp cord twisted around the base as 
shown in Figure 213 and screwed into the cutout are often 
used in place of fuses. The strand of cord is sometimes used 
to help out a fuse plug on an overloaded circuit. 

METER CONNECTIONS. 

Figures 214 to 216 show method of making meter con- 
nections in apartment buildings. Figure 214 shows con- 
nections for apartments where only one circuit is used for 
each apartment. In this case the meter is connected in the 
branch circuits after they leave their respective cutout blocks. 
While only three meters are shown in the figure any number 
of apartments could be connected in the same manner. 

Figures 215 and 216 show connections where two or more 
circuits are used in each apartment. Each meter leg is fused 
where it connects to the mains. After leaving the meter the 
main feeding the apartment is carried to the branch cutout 
blocks of which there can be any number. The design shown 
in Figure 216 is especially applicable to apartment buildings 
as a number of meters can be placed in a location where 
there is little head room as in the ordinary basement. 



4io 



MODERN ELECTRICAL CONSTRUCTION. 




u 
bfl 

E 



USEFUL INFORMATION. 



4H 




s-. 



412 



MODERN ELECTRICAL CONSTRUCTION. 



C 



•« 



n 



m 



yj 



♦ « i 







G 



D 







D 



^d 



ru^ 






3 



vo 

bo 

s 



USEFUL INFORMATION. 413 

Table of Carrying Capacity of Wires. 

The following table, showing the allowable carrying ca- 
pacity of copper wires and cables of ninety-eight per cent con- 
ductivity, according to the standard adopted by the American 
Institute of Electrical Engineers, must be followed in placing 
interior conductors. 

For insulated aluminum wire the safe carrying capacity is eighty- 
four per cent of t: at given in the following" tables for copper wire 
with the same kind of insulation. 

TABLE XO. I. 

Table A. Table B. 

Rubber Other 

Insulation. Insulations. 

B. & S. G. Amperes. Amperes. Circular Mils. 

18 3 5 1.624 

16 6 s 2,583 

14 12 ' 16 4,107 

12 17 23 6,530 

10 24 32 1O.380 

8 33 46 16,510 

6 46 65 26.250 

5 54 77 33,100 

4 65 92 41.740 

3 76 110 52.630 

2 90 131 66,370 

1 1<>7 156 83.600 

127 185 105,500 

00 150 220 

000 177 202 167.800 

0000 210 312 211.600 

Circular Mils. 

200.000 200 300 

300.000 270 4oo 

4Q0.0OO 330 500 

500.000 300 500 

600.000 450 680 

700.000 500 760 

800.000 550 840 

900,000 600 920 

1.000.000 650 1.000 

1.100.000 690 1.080 

1.200.000 730 1.150 

1.300.000 770 1.220 

1,400.000 si 6 1.200 

1,500,000 850 1,360 

1.600.0(H) S00 1.430 

1.700.000 030 1 .400 

1.800.000 070 1,550 

1,900,000 1.010 1.610 

2,000,000 1,050 1,670 



414 MODERN ELECTRICAL CONSTRUCTION. 

The lower limit is specified for rubber-covered wires to prevent 
gradual deterioration of the high insulations by the heat of the 
wires, but not from fear of igniting the insulation. The question of 
drop is not taken into consideration in the above tables. 



WIRING TABLES. 

The wiring tables, II-VI, are arranged in the following 
manner : For each size of wire and voltage considered there 
is given (under the proper voltage and opposite the number 
of the wire under the heading B. & S.) the distance it will 
carry i ampere at a loss designated at top of page. 

The same wire will carry 2 amperes only half as far at the 
same percentage of loss and again will carry 1 ampere twice 
as far at double the percentage of loss. 

From these facts we deduce the rule of these tables, which 
is: Multiply the distance in feet (one leg only) by the num- 
ber of amperes to be carried. Take the number so obtained 
and under the proper voltage find the number nearest equal to 
it. Opposite this number, under the heading B. & S., will be 
found the size of wire required. To illustrate : We have 22 
amperes to carry a distance of 135 feet and the loss to be al- 
lowed is 3 per cent at no volts. We therefore multiply 135 X 
22 = 2970, and turning to table IV, which is figured for 3 per 
cent loss, follow downward in the column under no until we 
reach the number nearest equal to 2970, which, in this case, is 
.3180 corresponding to a No. 7 wire. With this wire our loss 
will be slightly less than 3 per cent, while with No. 8 it would 
be somewhat in excess of 3 per cent. 

For three-wire systems using no volts on each side the 
column marked 220 volts should be used. The column marked 
440 volts is provided for three-wire systems using 220 volts 
on each side. The sizes determined will be correct for all 
three wires in both cases. 



USEFUL INFORMATION. 41 5 



The columns at the right, marked motors, are arranged 
in the same way, the only difierence being, for greater con- 
venience, they are figured in horse-power feet instead of am- 
pere feet. For this reason we multiply the distance in feet 
by the number of horse-power to be transmitted and divide 
by the percentage of loss, all other operations remaining the 
same as under lights. When any considerable current is to 
be carried only a short distance the wire indicated by the de- 
sired loss will very likely not have sufficient carrying capacity; 
it is, therefore, always necessary to consult the table of carry- 
ing capacities. 

RULE FOR WIRING TABLES. 

For lights, find the ampere feet (one leg) and under the 
proper voltage find the number equal to this or the next 
larger; opposite this number, in the column marked B. & 
S., will be found the size of wire required. 

For motors, proceed in the same way, using horse- 
power feet instead of ampere feet. 

For alternating currents, the results obtained by multi- 
plying the amperes (or horse-power) by the feet, should 
be multiplied by the following factors: 

1.1 for single-phase systems, all lights. 

1.5 for single-phase systems, all motors. 

For two-phase, four-wire, or three-phase, three-wire sys- 
tems, each wire need be only one-half as large as for 
single-phase systems and the number obtained may, there- 
fore, be divided by two. 



416 



TABLES. 







00t^C0i-<O TjIr^Oii-iO O *C CO O CJ i-< rt< i-( CO O O^t^t-hoO 
(NOOiOt-iTtl N>Ohh(M lOOO<NO 00 O iO -^ CO CO <N !M <M — « O 
O O O CO O OOCO^Ot^CO WNHHrH coooo oooooo 
(N-M^i-it-i ooooo ooooo ooooo oooooo 
coooo ooooo ooooo ooooo oooooo 
ooooo ooooo ooooo ooooo oooooo 


02 

« 

O 

h 
O 


U 

h 

O 
> 


o 
o 

o 


0^005 t-4 OOOOOO O0C5Tft^<M COi-HiOr^iO t^C5t^iOO-H 
NWHiQ^ iMrHrtOOM lO GC Ci LO O CO O rt< O "^ i-i I> i-i CO t^ O 
»0N05H^ GO CO O O O 0CCO'^l>I> t— i — t^ ^ — 1 1 — i O >-< CO !N tJ< OJ 

i-i !— I r-i CI <N CO "* 01>Oi'-H^ 00 CO O *0 CO Ci O CO O O O 

i-i i-h rHfNCNCO'tf ^lOON^OO 

i-i CM 


OOOOOO GO 01 C X -F X CO ^ X X OONOO oo^-^cocooo 

"T O O O d OCJLQ^M d i-h X X X X :N O CO t>. X CJ O X t^> O 

^»CNXH ^NMXiO lONr-lO 1 * "* CO 05 i-l lO OO^XOOrH 

,-H i-Hr-iO^CNCO tF iQ 1> O --H ^ X CM t^ CO t^ CO X tF X b- 

TH HrtNWCO CO^^lOO^H 
t-KM 


O 


CO O O ^ O NM^NO C3 X O CO CO OOOC^t 1 ^ (NCOM^IN 

H^NOIX lO-^COi-lCi C0050t^t>. CO X "* X "^ ]> lO i— 1 1> t}h 05 

i-l r-i tH CO CO C0^iOt>00 i-h TF t> CO X C>ONNH "tf X CO *0 i-h CO 

i-l i-t i-l CO CO CO^iOOX OiO<MCOI>T^ 


O 
i—i 


OOtO^OO X CO r-H X "tf CO i> CI X X lOiONO'O OOtjHtJhcOOCO 

CO CO tt< lO t>. OOi-^t^fM OCiO^OrH O^COOiCO O i-H lO Oi X t> 

i-HrHi-ioq <NC0"tfiOt> 05Hrj*oO COt>OCOl>iO 

i— I t— 1 1— < CS| CO CO C* CO O CO 

i-H 




u d 


<N -b- -rj< -CO -CO^ »OOOt^t> ONOOO OOOOOO 
r-H -r-i -^ -CO -r^iO CNC5CM L0t>-HC0r^ OCOOOiOlO 

i-irH i-Hi-iCOCOOO cocococooo 

1-4 


pqO 


rF 00 CO i-l O O X l> O iO ^MiNHO OOOOO OOOOOO 
,__, ^ ^ ,_ ,_, OOOOO OOOOOO 

oooo oooooo 
ooo oooooo 

OO lOOiOOOO 

coco co^^iooo 

t-iCO 




02 

M 

02 

H 

o 

►3 


O 

s 

o 

> 


o 


ocqcioo O^OCIX OOOO^X OOOOOO OOO^t^O^ 
MCW30H CC'fiO^ OCOO'OO CNWOO (N00ONOO 
0COC0O--H O CO M CO i> Tj^t^TtiO>0 t-hCO— <i-Hi-i T^^OCOt^Tfi 

i-l r-l rH CO (MCO^lOO OOOCOt^i-l ]> ^ CO r-H ,-t l-H i-H i-H CI CO b- 

i-ii-Hi-iCO CvJCO^iOO N00 03COO 

i-n'CO'tf 


O 


X O O O X O CO O «D Tj< 00^30N^ OXOOO^ -<tf O CO CO O CO 

HC10"*iO CO X CO t^ t- rtt'O^MM 00000X0 H^ro0>00 

Tjiiooooo cooi-toco co co t^ 10 b- 10 — i to 10 »o i> t^ x i-h x i> 

tH rH i-i CO CO CO ^ICCOOO WN-HOO lOOlOHHM 

T-HOO 


O 

1— 1 


OS CO CO O O »OHO30N TfiCO^^O-1 O^^ON NOOhiOh 

O O CO CQ CO Ot^OCOOO CI X l> O Ci 050XON lO t^ *-< X CO »0 

CO CO CO -<tf O O00OC0O i-h O CO CO CO t^iOt^t^-CM OCCOOitOOOO 

i-lrHrH (NC^CO^tO OOOOCSHO NON»OCH 

i-Hr-li-l t-H C-l IN <N lO O 




OO^COOO rt^t^rHTtiX OHLOHCO XCOOtNtN i-tOiCOCO-^X 

OiCMiOOiO 1-HOOC0C5 ONOhi* C^LOOCOOO Tf<MC0Or^"tf 

rHrH(N(M COCOtOOt^ O M O O "I MOOON ^OOOOOH 

HHHC41M CO^iOOt>> XOOfN-^X 

i-Hi-KN'* 



MODERN ELECTRICAL CONSTRUCTION. 



417 





03 

Is 


O 

O 


.002628 
.,002084 
.001653 
.001311 
.001040 

.000824 
. 000654 
.000519 
.000411 
.000326 

.000259 
.000205 
.000163 
.000129 
.000102 

.000081 
.000064 
.000051 
.0000431 
. 000036 

.0000308 

.000027 

.000024 

.0000215 

.0000108 

. 0000054 


Pk 
g 

« 

O 

H 
O 

8 


H 
O 

S 

O 

> 


O 

O 


OOOOOOOOO cMCOCOXCM COXX^"* COcMO^O Tt<X^OOcM 
lOTfUMr-iCi t}H CO CO O b- r-H>00^H<M CC005HOJ CO lO CO i> -* cM 

rHTtioocooo cdcoxcocm t^i>iototo ^tftfcmcm cco^-^aa 

HH1-1NW CO^»OI>Ci T-iTf00COO5 I>t»05 0^ X(N(OOOh 
HHHINN CO^iOI>00 05 H CM "tf 00 CD 





CO © X CM O CD Tl< CM © X © tJ< X © © OO^WIN CX0CCNO 

O CM O Ci ^t 1 i-H 00 1-1 OS CO lO CM © l> b- © ^ X t> »0 t^ «t CM I> lO CO 

00HTt*MM OOiOOOH O^COrHOi Oi CD G5 CM t-< t^ oo i> iO 1-1 CO 

hhhin (MCO"^»Ol> Gii-i^XcM OOcDiO-^iO iO © t^ X t^ Tt< 

,-Hi-Ht-icM CMCO^iO© N00OOHCC 




CM 

cm 


^O(M00O T+HcOOO^CM t*h © CM ^ "tf O O CO 00 00 <tf CM CM -^ 00 "* 
(MOOu^TtiCO OOicNCMOl CDlOOi-^T^ rf CO 05 CD 00 "tf *-* CO rf 00 00 
<N <N CO "* iO l>00'-H^I> CMXidOh- CMr-H^iOcM ON^hiMLO 

1-lrHrH CM CM CO Tfl lO I> Oi t-1 CO CD 00 t-H ^ I> Tf 00 




1—1 
1— 1 


©OXCMO CO^cMCOOO COt^OOCOCO O O ^ CM CM CO 00 00 CO CM CO 

*C t>» X i-i "tf NNOOiO^ © *-< Ci CO CO i-t C5t> O l> COC-IOOON'* 

i-HtH r-KMCMCOrtl lONOOHTt* X CM X CO O N^hNiOh 

i-Hi-I t-KNCNCOt^ t*h lO CD CD CO t>- 

rH (M 






CM -t^ -tH -CO -COtJH ICCOONN ONOWO OOOOOO 
rH «t-i .CM -CO «rt^iO CDI>050CM iONihCCN O CO CD 05 lo iO 

i-Hi-H i-ii-HCMCMCM COCOCOCOCCO 

r-l 


B. & S. 
Gauge 


tJ<C0CMt-hO OiXI>COiO ^COCM^O OOOOO OOOOOO 

T-lT-H^HrH^H OOOOO OOOOOO 

OOOO OOOOOO 

© © © OOOOOO 

lOO OOOOOO 

CM CO CO^^UOOC 

rHCM 




so 
a 
M 

! . (X 

1 § 

1 

.' CD i 

! @ 5 
•5 i 

1 "- i 


O 

§ 

> 





CM^^OCM OOOOOO (N^cMX© ©CMCMO© COOXXOX 
t^OOcOCO CM CM X © © © CO Ci © CO CM ^O t^ CM i-h IOCO(N^OO 
© i-i © CO CM COI^T^t^TtH © TF © i-H i-H CO r^ CM CO CM X © CO © "tf X 
THCMCMCO'<f IOCOXOCO ©i-H©^CO TjHOCOCMCM CM CM CO "* l> rj< 
rH^-i HiMiNCO^ lOCOXOCM ^CDXOOt-i 

,-H,_| r-lrtr-l(M^00 




CM 
CM 


COM (MOO O^OWOO COtMCO^X OCOCOOX XO^^O^ 

COiOCOOOH OCOt^iOttI ©C0©»O© CONMOO (MXCOCMOO 

XOCOOt-i © CO CM CO t> ^N^O»C t-h CO *-n t-h i-h ^^COCON^ 

TH^Hi-i<M (MCO^iOCO OOOCONH I> ^ CO t-i ^h ,-i h i-h (M CO l> 

»-ii-ii-i(M CMCO^^O© t^X©©0© 

r-H(MTjH 


O 


XCOCOOX OcMOCOrtH X © X X «tf OXXOrjn t^OCMcMO(M 

r-KMCOrtiiO M00NNN tJH CO ^ CM X XXCOX»0 HTfcOcCiOO 

■^»OOXO COOi-HCOCO CMCOh-iOr^ lOt-hiOlOiO NNOOhOON 

7-i rtrH (M<MC0 rJ<iOCOXO COI>t-iiOO lO O lO ^ ^h CO 

»-l i-It-I(McMCO C0TtHrt*»0OO 

^HCM 


\\"\ 


1 


tOXCOOO X^CMXCD OCMOcMCD COCDO^rfi cMXcOcOXCD 

a^rtOQ CM050COCS O^OiCMX lOOOOCO^ XiOCOX^OS 

W <!fl "5 CO !> O CM »C O^OhCO t)<hhO^ OOMChhM 

HH-i CMCMCO^iO COXOCMTtH CD Oi t-h r}H X CO 

rHi-irH i-H ^-1 CM CM "* 05 



4i8 



TABLES. 















r- 1 


00 iCOOx* 


(D 




OOT^COrHO 


^i*05tHCO 


O5iOC0O5CM 


rH^rHCOCO 


ON'I'hoiO 


-»j 


CM 00 iO i-i -^ 


CMlOi-HrHCN 


"OOONO 


OOOlOrHCO 


COCNCNCNrH© 


y< « 





OOOMO 


00 CO iO"tf CO 


CNCNrHrHrH 


OOOOO 


OOOOOO 


V o 


o 


CNCNrHrHrH 


OOOOO 


OOOOO 


OOOOO 


OOOOOO 


Ph 




OOOOO 


OOOOO 


OOOOO 


OOOOO 


OOOOOO 






OOOOO 


OOOOO 


OOOOO 


OOOOO 


OOOOOO 








NINONS 


COtHtHCNGO 


TfNCM^cO 


CiC0*OrHlO 


HNHiCOW 






o 


CONC0N"<* 


COiOiO^OO 


NCO00N00 


OOCOCNCO 


»OCOiOOHCO 






o 


Nhn^M 


TfffiNOOO 


lOrHOOCNCN 


i-htHCNCOtH 


OiOCON^OO 






*o 


i-iCMCMCO^ 


lOOOO i-h CO 


NCMNiOr^ 


COrHOlOCO 


NOOOSOrHCN 










T-H 1-H 


rHCMCNCO^ 


ONGOOCN 


"H/ CO 00 rH CM ^ 


fc 












i-i i— 1 


rH rH rH CM Tt< 00 




■^OCNOOO 


tHcOOO^CN 


TjHCOCM'*^ 


OOCOOOOO 


-^CNCN^X'* 


• 






Tfoo^ooco 


WNCO^iO 


00 CONOCO CO 


rfONOCN 


ONC5COCMO 


w 




<< 

a 

o 
> 


o 


CO CO rH CO CO 


CN CONON 


UOrHlOCM^ 


^OiO)i*N 


COCOiO00N»O 


Tft 


i-i i-i CM CM CO 


'tf'OOGOO 


CONi-iNtJH 


COrHcOrHt^ 


COOOCNlOrH 


s? 


•^ 




i-H 


tHtHCMCMCO 


^ lO CO 00 05 


rH CO T* CO CM lO 


CO 
tf 
O 














HHHHC0CD 




COO00CNO 


CO t!< CM CO 00 


co "^oo co co 


OO^CNCN 


CO 00 00 CO CM CO 




COCNCNN^ 


iOTjHOiCOOO 


OOOQOrHrH 


COtHt*iOC0 


rH(OTjHrHCON 


o 


COr^iOCOOO 


OCO CO i-H CO 


CO CN CO 00 CO 


00NCNCO<tf 


TJHIOCON^X 




CM 




i-H r-1 i-i CM CM 


COr^iOCOOO 


OPONOrf 


OOCMCOOrHCN 




CM 












£ 


















"tfiOCNOOO 


TjHcOCO^CM 


Oil— 1 Nt}< Tt< 


lOlOrHOOOO 


tJ< CN CN Ci 00 OJ 








OOOCOCOrH 


CO CO CM CON 


-*N^O»0 


rHCOrHOOO 


O"* CDNO rH 






o 


rH rH rH CM 


CMCO^iOCO 


XOWNH 


N^COOrH 


rH i— ( i— 1 rH CO N 






rH 






rHrHrHCN 


CMCO^iOCO 


N00 05OOO 






*H 










rHCM^ 






CM -N -^ 


•CO «CO^ 


iOcOONN 


ONOiOO 


OOOOOO 


IH Q 




iH -i-H -CM 


•CO "^iO 


CON050CM 


lONHCON 


OCOCOOi*OtO 


e3 o3 






• 


t-H i—l 


rH rHCNCNCN 


CO CO CO CO coo 


OO 






: : 






y-t 


is 




^00 CM HO 


OiOONCO^O 


TfCOCNrH© 


OOOOO 


OOOOOO 




1— 1 i— 1 i— 1 i-H i— 1 






OOOOO 


OOOOOO 


1 








OOOO 


OOOOOO 










OOO 


OOOOOO 










iOO 


100*0000 


«o 










CM CO 


CO«*T*iOOO 

rHCN 








OOCOCOOOO 


OCNOO-HH 


00 CO 00 CM -HH 


OOO OOO-* 


"^OCMCMO^ 






o 


OiOOl^Tt* 


00C5CN*OtH 


OOOi*OCOO 


00CNO00CN 


OO^ONO^ 






TF 


10-H050CO 


OONOCN 


TjHrHT*rHl> 


THrHrH TttCO 






^ 


CM CO CO »0 CO 


NOCNOO 


*OCNOrH«tf 


rH CO O CO CO 










1— li— 1 rH CM 


CNCO^iOCO 


OOOCNiOOO 


rH rj< NOrHCN 


CO 

Pi 












rH rHi— trH 


CNCMCNCOCOrH 




tjh OOOOOO 


OCOOQOCM 


^GO^rHCN 


OTt<Tt<OCN 


CMOCOCOOCO 


s 






lONOJNN 


CiTt<OCNCN 


tjh 05^0010 


TfcOO^cO 


Tt^CMOOO^OO 


CM 


• 


O 


(Ni0 05«5H 


OOCOOrH 


NOCNiOCO 


NONN5D 


rH CM Tt< TjH lO rH 


H 


w 


CM 


i-HrHrHCNCO 


CO^OCOOOO 


CNCOO*OCM 


OrHTj^COrH 


NfNNCOiOrH 





<M 




i-H 


i-H rH CM CM CO 


Tf U0CONO5 


OfMCOlOOrH 


i 












rH rH rH rH CO CO 




N05 00N 


lOCOO-^i-t 


CM Ci CM CM CO 


OCMCNOrH 


rHOOO CONOCO 




o 




CN OOOOOO 


Oi (M 00 i-h CO 


N^CNON 


NOCONN 


NHTt*"tNiO 


co 


> 


O 


CONOCNiO 


OOrHOO 


MOHNH 


CONCOCOOO 


OrHt^l^t^»C 


Eh 


H 


i— 1 i-H 


rHCMCOTflO 


COOOOCMCO 


O»O(N00iO 


CO i-i 00 CO CM to 


S3 




1— 1 






rH i— 1 i— 1 


CNCNCOCOrJi 


lOCOCONOO 


O 

H 














rHCO 




^(N-^OO 


CMrHCOCNT^ 


OCO*OCOC5 


^oococo 


CONOSOJCMTf 








ONNOO 


^00005 


OrHOOCOCN 


OOiONOCO 


CNOOONCN'* 






(M 


cnco^con 


OS rH 10 05 CO 


O00NOCO 


COOCNOO 


CO 00 "tf CM CN "^ 






O 




rHrHrHCN 


COCO^CON 


CXMlOOOrH 
rH i-H rH CM 


lOOOCNcOCM^ 
CMCMCOCON^ 

rH 



MODERN ELECTRICAL CONSTRUCTION. 



419 





Resis. 

per 

foot. 


^ 00 IO00"* 
OO^fOrHO ^ Tt< OS »H CO ©*OCOO»<N i-htJ<^hcOO ON^hOiO 
Cq00iOrHTj< c<l»Oi-Hi-i(N lOOCONO 00 O »0 "<*< CO COIN(NN-hO 
COO^COO OOOiO^CO (N (N r-i T-t »-h OOOOO OOOOOO 
(NfN^r-H^H OOOOO OOOOO OOOOO OOOOOO 
OOOOO OOOOO OOOOO OOOOO OOOOOO 
OOOOO OOOOO OOOOO OOOOO OOOOOO 


w 

z 

t-t 

CO 

« 


H 
O 


H 
O 

a 


> 




10 


ooooo "*<N<NOTt< (noooooo cot^oooo 00000003; 

HO^MOl 00l>I^COTt« C0iOt^(NTt< CO O 00 <M 00 tDH(OT*00J 

WX(C(ON (NiNCDMO tJHOhOO O3X03^iO O !>• 00 O 00 & 

<N<NC0^»O t^Oi»-i<*00 COOt^t^Ci ^^OOOOO CD^NOH^ 

i-i>-ItH <N<NC0tJ<iO NO-h^cO O <N iC 00 O ^ 

,-l^r-l ,H <N <N <N »0 i-< 



<* 


(NOOt^O (NOO^NCO C<1 00 O <N (N O O 00 t^ tJ< NtOtDN^IN 
C5 -tf "-1 00 GO COOC^OSCO i-HTfOOiOkO CNGOO^O iCOiCiClON 
NNOOlO'* COHOWM H00NWO5 Ci C^ Ci »0 CO «O^H«CC 
rH(N(NC0^ iOt^Oir-H^ 00(MOOOiO t^CO^OOO t-h CO iO t> "* 00 

i-HrH rH<N<NC0«tf ICN050W »0 t> O '-I CO O 





OOOOOO 00(MO00t^ 00<M^oOOO 00<MOO 00"*^00OX 
r£OOCJ<N 05 10-^00 (M^HOOOOOO 00<MCiCO:> OOfNOOOt^O 
rt<iOr>.00t> rJ<i><N00*O >CNhO^ ^MOJ'H'O 00 ^ 00 <N *0 t-i 

i-HrH<M(Nco ^ioi>os^h T^oo<Nt^(N t>. co oo ^ oo r-- 

1-1 HHINCACO CO "t Tf lO O ^ 


O 


CQOOTflO (N00INMCD <M 00 O <M <N OOOOrf^ <N O O <M r^ (N 
H^NMOO iOi*<DH05 C0<NOit^t>- C^OOrfOOTt* t^iO^Ht^TfO 
1-1 -t i-i CQ <N C0T^»Ot>«00 i-"T^^(M00 COiONN^ t*< 00 <N *C *~* (N 

HHH(N(N CCt^iOOOO ojonccn^ 

HHH1NIC 




00 


<N -h- •«* -CO -O^ lOOONN ONOiCO OOOOOO 
rH .1-1 -cq «C0 "^»C Ot>-050<N iOl>i-iC0t>- OWOOS'CiC 

i-HtH iHtH(N(N(N COCOCOCOOO 


CQ 

PQO 


rt«C0e*i-i© 0500tN.O»0 ^MNHO OOOOO OOOOOO 
i-i 1-1 1— 1 tH i-h OOOOO OOOOOO 

OOOO OOOOOO 

OOO OOOOOO 

iOO "OCCCCO 

<NC0 CO^TjHiCOC 




w 
M 
W 
(V 

to 

h 

a 



►3 




s 



> 


O 
<* 


'* OOOOOO OOO00N ^00<*O<N O^TfiOM <N©0 0©<0 
^0(N<NO ^iO(D003 00<NOO'-tt>' ""* O "tf ^ CO h(N»0 050^ 
C0<NC0I>«* O^Oi^Oi 0>Oi05(N(M OiOiOO-tf N05CD(NX2 
COtJUOOOO OC0©hO CO<NCOOOO 00 b- <N ^ -^ »0 iO O O "* S 
.-itHi-h<N<N CO^iOOOO OCOt^O-^ 0OIN(DChS 
HHHCIIN (MCOCO^OOi-H 


O 


(MtJit^O(N OOOOOO (N^iMOOO 0<N<NOO O O 00 00 O 00 
t^OOOCO NN00O05 CJOC5OC0 <N iO h- <N i-t lOCN^cc 
OtHOCOiM C0l^^t>.Tt< Oi'^O'-H'-i COt^(NC0<N 00 O CO O r^ 00 
»-h<M<NC0^ iOOOOOCO Oi-hO-^CO -^ 00 O <M <N <N OQ CO Tf r^ x 

rHi-H i-HC^CMCO'^ lOOOOOlN TjHO00OO«-H 
,-lrH y-i 1-4 rt (M t^ X 


O 

r-i 


ONWOO O^OiNOO 0<MOrt<00 OOOOOO OOO^'^O'* 

COiOC000i-t OOt^iO"^ 05C005VOO or^cooo N00ONOC 

OOOCOOi-H OC0<NC0t>- Tfi|>T^OiO hCOh^h T*< rj< O CO I>- ^ 

THr-lrHC^ C<l CO t}< lO O 00OWNH t^ T^ CO — < ^H HHHNWN 

i-Ht-htH<M <NCO^iOO l>XOOOO 

1— t C^ "^ 




(MOCMOO OOO^OCVI O-^O^fN (NCNJO0000 t*o<n<no<n 

oocooo loooocooi oooooTft^. hhcoinoo i-H co r^ a 

CO^OOOO N>00>Oh OOWOh O5(NC0i-H00 b-»OCOCO<NiO 

r-t HHMNM ^IQOOOO (NOO^OO CO 00 CO 00 O <N 

iH »HtHW(N<N COCO^'tOiOS 

1-H 



420 



TABLES. 



v. <x> c 

<v z~ o 



OCCOCOO 
CM CM rH rH rH 

ooooo 
© o © © © 



Tt<THOrH© 
NiOHHlN 
X©O"tfc0 

©©©©© 
©©©©© 
©©©©© 



oocoocm 

(MWHHH 
©©©©© 

OOOOO 

©©©©© 



XOOrfcO 

©©©©© 
©©©©© 
©o©c© 
©©©©© 



00 nzao-rn 

COCMCMCMrHO 

ccccco 
© © © © © o 
©©©©©o 
©©©©©o 







oo©oo 


o © o © o 


OOOO© 


OOOOO 


oooo©o 




© 


O CM O O "tf 


©OOCMX 


©rHOGOrH 


© © CM CO CM 


0CO00NO© 




© 


GO © O t^ CM 


H OOr* rH 


cmo^nx 


CONON 


OXCHM^ 
OOOhnS 

^OOrHOCH? 




O 


CMC0^f<Ol> 


©rHrHoOCO 


©©©GO CO 


CO GO X O © 








r-lrHr-ICM 


CMC0t*OI> 


Oir^rT t^rH 












7-Hr-^i-iC^ 


CMCMCOCOt^r-H 






©©©o© 


©©©©© 


©©©©© 


©©©©© 


©©©©©o 






^©CMOO© 


TfiOGO^CM 


t« ©CMtFth 


©©©00 00 


"*CMCMrHoo^ 


w 


© 


(MGCO^CD 


©©CMCMO 


©OOt*tH 


tH © o © X 


O !> Tt< rH CM £g 


o 




"* 


CMCMC0"tf O 


I> X rH r* ^ 


CMXOON 


CM r-. t* O CM 


^ 




rH rH rH 


CMCMCOthiO 


NOhWcD 










rHrHrH 


rH CM CM CM O S 




©©©©© 


©©©©O 


©©©©© 


©©©©© 


©©©©©© 




© © GO CM © 


©T*CM©X 


© Tt< GO © © 


© © <* CM CM 


COCXCNO 


© 


Ot^XrHTH 


b~ CM GO O t* 


©rHOCOCO 


rHOJNON 


CO CM © X l> -tf 




CM 


rH.rH 


rH CM CM CO t* 


Ot»XrHTH 


XCMXCOO 


NTtHNlfjH 




CM 






rHrH 


r-CMCMCOTH 


rfiOOCDCON 

rHCM 






OOOOO 


OOOOO 


coooo 


o o o© © 


© © © o © o 






^ t^CMOOiO 


^©OOCM 


OX^t*o 
Tttt^CMGOO 


CM CM 00 00 00 


T* Nt>©C0© 




© 


i-i rH CM CM CO 


«#Ol>XrH 


ON rHrHrH 


X O CM © O X 




rH 




1-H 


rHrH CM CM CO 


"tf ot>oo© 


r-t CO O © CO N 




T-H 








y-i 


r-i r-4 y-< <r* CO © 



C a 



CM -l> -^ 

'rH -CM 



©rH 

^ o 



OOONN 
©l>OOCM 



ONOOO 

Ol>rHC0l> 
rHrH CM CM CM 



©©©©©© 

ocooooo 

CO CO CO CO©© 






rfcOCMrHO OOONCOO rfCOCMrHO 



©©©©O 
©©©©© 

©©©o 
©©© 

OO 
CM CO 



©©©©©© 
©©©©©© 
©©©©©© 
©©©©©© 
OOOO©© 
CO-^ rf OO© 

rHCM 



03 




K 




« 




W 




(h 





<* 


«! 


£ 




M 


O 


02 
h 


> 


H 




O 








H-l 





©©©©© 

X © © © X 

rHCM©T<0 

■*o©x© 



©©©©© 

©CM©©tH 
COXCMI>l> 

CO©rH ©CO 
rHrH CM CM CO 



©OOOO 
X©Xt>r« 
-tH©thcmx 
CMCOt^Ot^ 

TtOOOOO 



©o©©o 

©XXOrH 

xx©xo 

OrHOOO 

conhoc 

rHrH CM CM CO 



©©O©©© 
^©CMCMg^ 

rHTHCO©^ . 

OOO^So 

COrJlTHlOrHCM 



O©©©© 

ococoo© 

O © CO CM CM 
CMCMCOtHO 



OO©©© 

CHOQ0N 
©rjH©COX 
©X©C0© 



©©©OO 
t* CO rH CO CM 
NOONCOO 
rH©COCMCO 

CMCMCO^O 



o©©©© 

Oh/h^on 
©OXOi>. 
NONNN 
©X©CMO 



©©©©OO 

i> © © rH to rr 

O 1> rH 00 Ol ^ 

©CO 0500,2 
l> X CM O O o 
rH CM CM CMO<=< 



OOOOO 

TfrH©©^ 
OC0©rH© 
rH rH rH CM CM 



ooo©o 

CMO©OC0 
COCMCO©^ 
C0t«O©X 



ooo©o 

CMrHl>CM© 

co^oococa 

OCO©rH© 
rH rHrH CM CM 



o©©©o 

ONW OX 
© ©© ©CO 
CO CM CO CO© 
C0t*O©1> 



oooooo 

X OX©CM O 
CMX 0©©CM 

OJrHrHt^THOS 

X©rH CM OO 

rH rH rH CM O 



©©©©© 

© CM © © O 
tH©1>OCM 



©OO©© 
I>XOi>© 

0©OrH<JJ 
rHrH CM CO CO 



OOOOO 

oor^OrH 
©cooot> 

0©1>©CM 



©o©©o 

T*©0©rH 

HN^HH 

©ooc© 

rH CM CM CO CO 



OOOO©© 
0^©©t>"# 

CM rH ^1 ^H CO l> 

(M00'/ ©O© 

tHtHio©CMt* 

rH CM 



MODERN ELECTRICAL CONSTRUCTION. 421 

It is often necessary to reinforce mains which have become 
overloaded. It is quite usual though often very incorrect, to 
choose by the table of carrying capacities a wire of such size 
that the rated capacity of it and the wire to be re-enforced 
shall be equal to the load. Small wires have proportionately 
a much greater radiating surface than larger ones and there- 
fore their carrying capacity is proportionally greater. In order 
that a wire connected in parallel with another wire shall carry 

C. M. X a 

a certain current, its circular mils, must be equal ■ 

A 

where C. M. stands for the cross-section of the larger wire in 
circular mils and A for the current to be carried by it, while 
a is the current to be carried by the extra wire. Table No. 
VII is calculated from this rule and shows the size of wire 
necessary to re-enforce another overloaded to a certain per 
cent as indicated in the top row. For instance, a 0000 wire 
overloaded 40 per cent requires re-enforcement by a No. 1 ; a 
No. 3 wire overloaded 20 per cent requires a No. 10 wire. 
Where large wires are re-enforced in this way by smaller ones 
great care must be taken that the larger w T ire cannot be acci- 
dentally broken or disconnected, since in such a case the whole 
load would be forced over the smaller wire and would likely 
result in a fire. The two wires should be securely soldered 
together. 

TABLE NO. VII. 



Am- 
peres. 


B. &S. 


10% 


20 


30 


40 


50 


60 


70 


80 


90 


100 


210 


0000 


6 


4 


2 


1 





00 


000 


000 


0000 


0000 


177 


000 


8 


5 


3 


2 


1 





00 


000 


000 


000 


150 


00 


9 


6 


4 


3 


2 


1 








00 


00 


127 





10 


7 


5 


4 


3 


2 


1 


1 








107 


1 


10 


8 


6 


5 


4 


3 


2 


2 


1 


1 


90 


2 


11 


9 


7 


6 


5 


4 


3 


3 


2 


2 


76 


3 


12 


10 


8 


7 


6 


5 


4 


4 


3 


3 


65 


4 


14 


11 


9 


8 


7 


6 


5 


5 


4 


4 



422 



TABLES. 















•3/jg 








ejiiH oj ^on 999 *sino* 








-SXS 9IIA-99IIfl UOStpg JO 








s2up*ds JOi — -axOS 






9 


A 








s * 


0- - w w * 


• www 






2 « 


a - - - . - 


• www 






JS 








GO 

*3 


.2^ 


^^ *** as* 






w g 


r- i-( M N W CM -HiHr-)** 




o 


»-, 










M 






GQ 


.2 "S 






H 


n 


"S "** 






D 


• 

CM 


o3 "o 


O. « • • . 




O 
i 


i-t 


o-a, 

GO « 


.2" " " " " 


• www 


P 




l'i 


*«*:*:*.* 


^a? ^ 




S «- 


-- iH CM CM CM CO 


O 




." fa. 
CO 






Q 




« O 










fc 










< 




«9 






gq 




al 


d 




H 
o 


GQ 

GQ 

0> 
1— ( 




©w <• • m m m m w ■ 

«rc-H-H CM CM CM cf?e*?-«;-H 


M 


o 


PQ 






£ 


GQ 








GQ 


*J? 








O 


"•** J-i 








> 

in 


2j5 

as 

CO <s> 


-q 

jjs r 3 r : 


w : : w 


p 


tH 


9*3 


"^^a? 


■f?iHrf tH 


> 

M 




i-H -H -M ©* CM « 




no 






P 




S'S 






55 














r— : 






GQ 
GQ 


Hi 


: cq 

CO 
0) 










e- « 


F^ 








t- GQ 










a> 


£ 








,„ ^ 


- • 








GQ © 


GO Q<w w 

© »« w 








Amper 
-35 Am] 
■100 
■300 
600 
1000 « 
















Sooo 








Ol1?OHi-H^ 


r^H O rn ■•< '" H 








~-i-HCfl©OG 
r-CQ *C 














fe 












XI 










a J 


0- - 


w w 








a- • 


w w 






CO 


N« 












3m 


^^? 


S*^! 






.0 


H g 


ihwhcq 


1 »— ( T^ 


^3 




r> 


E 
00 






q 




O 








lO 


*S >» 


.a 








CM 


^ 


0. - 


w • 


^ 


0D 


CM 

1-H 


-5 

CO -3 

. p-. 






nr 




2 p*" 


rl-lti 


J-i-r-i 








«o 








>— ■ 












JU 




CQ • 
GO • 


CQ • 
CQ • 




a. 




© s 


•S-. 




ti 






^2 




H 




CQ © 


2? a 




0) 




O ft. 

©a 
3^1 


2a 




O 










si^ 


2^ 




O 










H 












H- 















CO 

CQ 




-q 

0- - 
q- * 


5 r 




ro 


0) 


.2^ 
* g 








2 


"^ 


S^ 


M^ 




H 

2 


u 









.q 





CO 








q 


<! 


4- 


2^ 








H 


tS 


43 E 

4 el 






^ 


Z 


S.£ 


CJw w 






U 


ua 


00 • 


q* • 


w w 




u 

CQ 

P 


-H 


11 


^-h2 »-h 








a'S 














O 










• 


cc 








* . 


GO • 
© • 


J 




Cfl 




co • 


GQ • 

q : 


w 

S5 




CQ 






fa : 












< 




© 


S2 


is* 3 






si- 




CI 












So 


2«D 






<3cKnr: 


*><2 


sa 






one 


Ho^ 


s d 






fHiHCN 


0Q HH 
P 


a 













(* 


GO 









GQ 
•3 

O 

> 

O 

IC 
CM 

1 

«o 

C<1 






CQ 

GO 

t-> 



CO 
«a 

O 
> 


,q 

: 
q 




Separation of Branch Bars. . 
Separation Between Main 
and Branch Bars 



MODERN ELECTRICAL CONSTRUCTION. 
DIMENSIONS OF COPPER WIRE 



423 



DO 

©CO 


1 




Weights 




.a © 




93 

03 3 r^ . '. 






0&«M 


Num 
B. & 
Gaug 


1000 feet 


Mile 


o2 


0000 


460. 


211,600. 


641. 


3,382. 


.051 


000 


410. 


168,100. 


509. 


2,687. 


.064 


00 


365. 


133,225. 


403. 


2,129. 


.081 





325. 


105,625. 


320. 


1,688. 


.102 


1 


289. 


83,521. 


253. 


1,335. 


.129 


2 


258. 


66,564. 


202. 


1,064. 


.163 


3 


229. 


52,441. 


159. 


838. 


.205 


4 


204. 


41,616. 


126. 


665. 


.259 


5 


182. 


33,124. 


100. 


529. 


.326 


6 


162. 


26,244. 


79. 


419. 


.411 


7 


144. 


20,736. 


63. 


331. 


.519 


8 


128. 


16,384. 


50. 


262. 


.654 


9 


114. 


12,996. 


39. 


208. 


.824 


10 


102. 


10,404. 


32. 


166. 


1.040 


11 


91. 


8,281. 


25. 


132. 


1.311 


12 


81. 


6,561. 


20. 


105. 


1.653 


13 


72. 


5,184. 


15.7 


83. 


2.084 


14 


64. 


4,096. 


12.4 


65. 


2.628 


15 


57. 


3,249. 


9.8 


52. 


3.314 


16 


51. 


2,601. 


7.9 


42. 


4.179 


17 


45. 


2,025. 


6.1 


32. 


5.269 


18 


40. 


1,600. 


4.8 


25.6 


6.645 


19 


36. 


1,296. 


3.9 


20.7 


8.617 


20 


32. 


1,024. 


3.1 


16.4 


10.566 


21 


28.5 


812.3 


2.5 


13. 


13.283 


22 


25.3 


640.1 


1.9 


10.2 


16.85 


23 


22.6 


510.8 


1.5 


8.2 


21.10 


24 


20.1 


404. 


1.2 


6.5 


26.70 


25 


17.9 


320.4 


.97 


5.1 


33.67 


26 


15.9 


252.8 


.77 


4. 


42.68 


27 


14.2 


201.6 


.61 


3.2 


53.52 


28 


12.6 


158.8 


.48 


2.5 


67.84 


29 


11.3 


127.7 


.39 


2. 


84.49 


30 


10. 


100. 


.3 


1.6 


107.3 


31 


8.9 


79.2 


.24 


1.27 


136.2 


32 


8. 


64. 


.19 


1.02 


168.5 


33 


7.1 


50.4 


.15 


.81 


214.0 


34 


6.3 


39.7 


.12 


.63 


271.7 


35 


5.6 


31.4 


.095 


.5 


343.6 


36 


5. 


25. 


.076 


.4 


431.6 



424 TABLES. 

Table giving the outside diameters of rubber covered wires for use on 
voltages less than 600. 



Size 


Solid 


Solid 


Strand- 


Strand- 


B. &S 
Gauge 


Wire 


Wire 


ed Wire 


ed Wire 


Single 


Double 


Single 


Double 


Braid 


Braid 


Braid 


Braid 


0000 


47-64 


54-64 


52-64 


59-64 


000 


41-64 


46-64 


48-64 


55-64 


00 


38-64 


43-64 


43-64 


48-64 





36-64 


40-64 


40-64 


45-64 


1 


33-64 


37-64 


37-64 


42-64 


2 


29-64 


33-64 


32-64 


37-64 


3 


27-64 


31-64 


30-64 


34-64 


4 


25-64 


29-64 


27-64 


31-64 


5 


24-64 


28-64 






6 


22-64 


26-64 


24-64 


28-64 


8 


18-64 


22-64 


20-64 


23-64 


10 


16-64 


20-64 


18-64 


21-64 


12 


15-64 


19-64 


16-64 


20-64 


14 


14-64 


18-64 


15-64 


19-64 


16 


10-64 


13-64 






18 


9-64 


12-64 







Solid 
Twin Wire 



54-64x101-64 
46-64x 87-64 
43-64x 81-64 
40-64x 75-64 
37-64x 70-64 

33-64x 62-64 
31-64x 58-64 
29-64x 54-64 
28-64x 52-64 
26-64x 49-64 

22-64x 41-64 
20-64x 37-64 
19-64x 35- 
18-64x 33- 
13-64x 24-64 
12-64x 22-64 



Stranded 
Twin Wires 



-64 
-64 



59-64x111-64 
55-64x103-64 
48-64x 91-64 
45-64x 85-64 
42-64x 79-64 

37-64x 69-64 
34-64x 64-64 
31-64x 58-64 

28-64x 52-64 

23-64x 42-64 
21-64x 38-64 
20-64x 36-64 
19-64x 34-64 



Table giving 


the outside diameters of rubber covered wires for use on 


Voltages between 600 and 3500. 








Size 
B. &S. 
Gauge 


Solid 


Solid 


Strand- 


Strand- 






Wire 


Wire 


ed Wire 


ed W T ire 


Solid 


Stranded 


Single 


Double 


Single 


Double 


Twin W 7 ire 


Twin Wire 


Braid 


Braid 


Braid 


Braid 






0000 


49-64 


56-64 


53-64 


61-64 


56-64x105-64 


61-64x114-64 


000 


46-64 


53-64 


50-64 


57-64 


53-64x 99-64 


57-64x107-64 


00 


41-64 


46-64 


47-64 


53-64 


46-64x 87-64 


53-64x 99-64 





38-64 


43-64 


42-64 


46-64 


43-64x 81-64 


46-64x 88-64 


1 


35-64 


40-64 


39-64 


43-64 


40-64x 75-64 


43-64x 82-64 


2 


33-64 


38-64 


36-64 


40-64 


38-64x 71-64 


40-64x 76-64 


3 


31-64 


36-64 


34-64 


38-64 


36-64x 67-64 


38-64x 72-64 


4 


29-64 


33-64 


31-64 


35-64 


33-64x 62-64 


35-64x 66-64 


5 


2o-64 


32-64 






32-64x 60-64 . 




6 


27-64 


31-64 


28-64 


32-64 


31-64x 58-64 


32-64x 60-64 


8 


24-64 


28-64 


26-64 


30-64 


28-64x 52-64 


30-64x 56-64 


10 


22-64 


26-64 


24-64 


28-64 


26-64x 48-64 


28-64x 52-64 


12 


21-64 


25-64 


22-64 


26-64 


25-64x 46-64 


26-64x 48-64 


14 


20-64 


24-64 


21-64 


25-64 


24-64x 44-64 


25-64x 46-64 



NOTE. — These figures are taken from data furnished by one of the largest 
manufacturers of wire and are believed to be of at least as great dimensions 
as any standard wire on the market. Judgement must be used in applying 
these dimensions as the same size wire B. & S. gauge, of different makes 
often varies considerably in outside diameter. 



MODERN ELECTRICAL CONSTRUCTION. 



Outside Diameters of Rubber 
Covered Cables. 



425 

Outside Diameters of Weather- 
proof Wire. 



Capacity in 


Diameter 


Cir. Mils. 


over Braid 


1,500,000 


113-64 


1,250,000 


107-64 


1,000,000 


97-64 


950,000 


95-64 


900,000 


94-64 


850,000 


93-64 


800,000 


89-64 


750,000 


87-64 


700,000 


83-64 


650,000 


81-64 


600,000 


79-64 


550,000 


76-64 


500,000 


73-64 


450,000 


68-64 


400,000 


66-64 


350,000 


64-64 


300,000 


61-64 


250,000 


59-64 



Dimensions of Unlined Conduit. 



Nominal 


Actual 


Actual 


Thick- 


Internal 


Internal 


External 


ness of 


Diam. 


Diam. 


Diam. 


Walls 


inches. 


Inches. 


Inches. 


Nearest 
64th 


i 


17-64 


26-64 


4-64 


1 
4 


23-64 


35-64 


5-64 


a 

8 


31-64 


43-64 


6-64 


X 
2 


40-64 


54-64 


6-64 


I 


52-64 


67-64 


7-64 


1 


67-64 


84-64 


8-64 


H 


88-64 


106-64 


9-64 


H 


103-64 


122-64 


9-64 


2 


132-64 


152-64 


10-64 


2* 


157-64 


184-64 


13-64 


3 


196-64 


224-64 


13-64 



Size of 


Outside Diameters. 


Wire 


Solid 


Stranded 


1,000,000 




108-64 




900,000 





103-64 


800,000 





100-64 


700,000 





94-64 


600,000 




85-64 




500,000 





80-64 


450,000 





76-64 
73-64 


400,000 


— j — 


350,000 





64-64 


300,000 





62-64 


250,000 





58-64 


0000 


50-64 


55-64 


000 


47-64 


51-64 


00 


39-64 


43-64 





36-64 


39-64 


1 


32-64 


35-64 


2 


30-64 


33-64 


3 


27-64 


30-64 


4 


25-64 


28-64 


5 


22-64 


24-64 


6 


20-64 


22-64 


8 


17-64 


18-64 


10 


16-64 




12 


14-64 




14 


12-64 




16 


10-64 




18 


8-64 





Dimensions of Lined Conduit 



Nominal 


Actual 


Actual 


Internal 


Internal 


External 


Diameter 


Diameter 


Diameter 


Inches 


Inches 


Inches 


i 


32-64 


54-64 


3 

4 


45-64 


67-64 


1 


58-64 


84-64 


H 


80-64 


106-64 


li 


90-64 


122-64 


2 


115-64 


152-64 


2+ 


144-64 


184-64 


3 


176-64 


224-64 



.126 



TABLES. 
DIMENSIONS OF PORCELAIN KNOBS. 



Trade 
No. 


Height 


Diameters 


Hole 


Groove 


Height of 
Wire 





2i 


3 


H 


1 


* 


1 


3 


2| 


7 


f 


u 


2 


2 


2 


* 


I 


1 


3 


H 


2 


A 


1 


I 


3J 


1 2 


2 


A 


1 


4 

4* 


if 


1* 




i 

1 


o 


li 


i 


1 


A 


1 


5i 


1A 


i 


JL 

4 


A 


1 


7 


1 


i 


i 


A 


1 


9 


. H 


1 


8 


A 


i 


10* 


if 


if 


t 


l 



DIMENSIONS OF GLASS KNOBS. 



Trade 


Height 


Width 


Size of 


Size of 


Number 




Hole 


Groove 


1 


H 


1* 


| 


3 


1* 


If 


H 


| 


§ 


2 


If 


2 


| 


A 


3 


21 


2 


f 


A 


7 


2| 


2 


1 




8 


3| 


2| 




1" cable 



SIZES OF PORCELAIN TUBES. 



Internal 


Shortest 


Greatest 


Outside 


Diameter 


Length 


Length 


Diameter 


Inches 


Obtainable 


Obtainable 




A 


* 


24 


A 


I 

f 


i 


24 


■ 


* 


1 

1 


24 
24 


: 


1 


f 


1 


24 


1A 


1 


l* 


24 


1A 


u 


2* 


24 


Iff 


11 


2* 


24 


2A 


24 


24 


2A 


2 


2* 


24 


2H 


2i 


2* 


24 


3A 


2i 


2* 


24 


3H 



DIMENSIONS OF MOULDINGS. 



Size of Groove 


Size of Wire 


Size of Groove 


Size of Wire 


7-32 

5-16 

13-32 

9-16 


14-12 B. & S. 

10- 8 B. & S. 

6-5-4 B. & S 

3-2-1-0 B. & S. 


3-4 

7-8 
1 
1 1-4 


0-0000 Stranded 
250 . 000 C. M. 
500.000 C. M. 
750.000 C. M. 



MODERN ELECTRICAL CONSTRUCTION. 
DIMENSIONS OF CLEATS. 



427 



One- Wire Cleats. 

Duggan Cleat. 
No. 4 holds wires 16-8 B. & S. 



No. 


7 M 


No. 


5 M 


No. 


6 " 


No. 


8 M 


No. 






6-2 " 
2-00 

000-300,000 C. M. 
400,000-800,000 C. M. 
900,000-1,200,000 C. M. 



Brunt Cleat. 
Stand. 
Number Width Length Groove 

328 f 2 $ holds wires 16-5 B. & 

329 1 2i § " " 8-3 

331 H 2J H - M 3-00 

330 1| 2\ \ " M 4-1 

332 H 2i ff " " 0-0000 



Two and Three- Wire Cleats. 
Brunt. 

No. 334 2-wire holds wires 16-8 B. & S 

No. 337 3 wire " " 16-8 B. & S 

Duggan. 

No. 3 2-wire holds wires 16-8 B. & S. 

No. 2 2-wire M M 6-00 B. & S. 

No. 1 3 wire " M 16-8 B. & S. 

Pass & Seymour. 

No. A-3 2-wire holds wires 14-12 B. & S. 

No. 3 2-wire M " 14- 6 B. & S« 

No. A-43 3-wire * 4 M 14-12 B. & S. 

No. 43 3-wire " " 14- 6 B. & S. 



428 



TABLES. 
DIMENSIONS OF IRON SCREWS. APPROXIMATE. 



Trade Number 


Diameter in 


Nearest B. & S. 


Greatest Length 




Fractions 


Gauge 


Obtainable 





7 
T25 


15 


a 


1 


y 
T2S 


14 


i 


2 


5 

64" 


12 


7 
8" 


3 


A 


11 


ll 


4 


A 


9 


H 


5 


A 


8 


2£ 


6 


17 
TZS 


7 


3 


7 


& 


7 


3 


8 


3 5 2 


6 


4 


9 


ii 


5 


4 


10 


if 


5 


4 


11 


&f 


4 


4 


12 


27 
T2S 


4 


6 


13 


29 
T'3 


3 


6 


14 


15 
B4 


3 


6 


15 


i 


2 


6 


16 


17 
B4 


2 


6 


17 


A 


1 


6 


18 


H 


1 


6 



DIMENSIONS OF COMMON NAILS. APPROXIMATE. 



Trade 


Diameter in 


Nearest B. & S. 


Length in 


No. 


Number 


Fractions 


Gauge 


Inches 


per lb. 


2d 


9 
T28 


13 


1 


875 


3d 


A 


12 


u 


565 


4d 


& 


10 


H 


315 


5d 


h 


10 


U 


270 


6d 


& 


9 


2 


180 


7d 


& 


9 


2i 


160 


8d 


17 
T2S 


8 


2i 


105 


9d 


17 
TZ8 


8 


2f 


95 


lOd 


19 
T28 


7 


3 


70 


12d 


t¥s 


6 


3i 


60 


16d 


S 8 3 


6 


3i 


50 


20d 


2 5 
T5S 


4 


4 


30 



Fine Nails 



2d 
3d 
4d 



15 
13 
12 



1 
1* 

14 



1350 
770 
470 



MODERN ELECTRICAL CONSTRUCTION. 

RATING OF MOTORS. 
Full Load Currents. 



429 



H. P. 


110 VOLTS 


220 VOLTS 


500 VOLTS 


1 


1.9 


.95 


.42 


1 


2.7 


1.35 


.62 


h 


5. 


2.50 


1.15 


I 


7.5 


3.75 


1.70 


1 


9.2 


4.60 


2.10 


2 


17.5 


8.75 


4, 


3 


24.6 


12.30 


5.60 


4 


32. 


16. 


7.50 


5 


40. 


20. 


9.20 


7h 


57. 


28.5 


13. 


10 


76. 


38. 


17.5 


15 


110. 


55. 


25. 


20 


144. 


72. 


' 34. 


25 


176. 


88. 


40. 


30 


210. 


105. 


49. 


35 


250. 


125. 


57. 


40 


280. 


140. 


65. 


45 


320. 


160. 


75. 


50 


350. 


175. 


80. 


60 


430. 


215. 


100. 


75 


520. 


260. 


120. 


100 


700. 


350. 


160. 


125 


880. 


410. 


210. 


150 


1056. 


530. 


245. 


175 


1230. 


615. 


280. 


200 


1400. 


700. 


325. 



RATING OF INCANDESCENT LAMPS. 





110 VOLTS 






220 VOLTS 




C. P. 


Watts 
18 


Amperes 


C. P. 


Watts 


Amperes 


4 


.16 


8 


36 


.16 


6 


24 


.22 


10 


45 


.20 


8 


30 


.27 


16 


64 


.29 


10 


35 


.32 


20 


76 


.35 


12 


40 


.36 


24 


90 


.41 


16 


56 


.51 


32 


122 


. .55 


20 


70 


.64 


50 


190 


.86 


24 


84 


.76 








32 


112 


1.00 








50 


175 


1.60 









430 TABLES. 

The Cooper- Hewitt Mercury Vapor lamp requires a current of about 3.5 
amperes. 

The Nernst lamp consumes 88 watts per glower; for a 6 glower, 110 volt 
lamp, about 4.8 amperes. 

Series miniature lamps, operated 8 in series, on 110 volts, require a current 
of about .33 amperes for 1 candle power lamps, and 1 ampere for 3 candle 
power lamps. 



Tables showing the currents which will fuse wires of different sub- 
stances. 



B. &S. 
Gauge 


Diam. 


Copper 


Aluminum 


German 
Silver 


Iron 


10 
12 
14 


102. 
81. 
64. 


333. 
236. 
165.7 


246.5 
174.4 
122.8 


170. 
120.5 
84.6 


102.3 
72.6 
50.9 


16 
18 
20 


51. 
40. 
32. 


117.7 
81.9 
58.5 


87.1 
60.7 
43.4 


60.1 
41.8 
29.9 


36.1 
25.2 
18. 


22 

24 
26 


25.3 

20. 

16. 


41.1 
28.9 
20.7 


30.5 
21.5 
15.3 


21.0 
14.8 
10.6 


12.4 
8.9 
6.4 


28 
30 
32 


12.6 
10. 

8. 


14.5 

10.2 

7.3 


10.7 
7.6 
5.4 


7.4 
5.2 
3.7 


4.5 
3.1 
2.3 


34 
36 


6.3 
5. 


5.1 
3.6 


3.8 

2.7 


2.6 

1.8 


1.6 
1.1 



INDEX 



PAGB 

Acid Fumes 98-182 

Alternating current systems 35 

Amperes 13 

Arc lamps, construction of 364 

Arc lamps, installation of 141-146-233 

Arc lamps, theater 254 

Armored cable, construction of 315 

Armored cable, installation of 198 

Armored cable, metallic sheaths to be grounded 104-198 

Attendance 73 

Auditorium 262 

Auto-starters 84-92-369 

Balancing coils on three-wire systems (See Reactive coils.) 

Base frames, generators and motors 47-78 

Batteries, storage and primary 27-98 

Bells 19 

Bell wires 380 

Bonds, rail in car houses 283 

Border lights 246 

Boxing, where necessary 144-177-293 

Bunch lights 257 

Burglar alarms 380 

Burrs and fins, fixture work 219 

Bushings at entrance to building 103-289-381 

Bushings for wires 129-175-191-321 

Bushings for lamp sockets 232 

Bus bars 60-63 

Bus bars, carrying capacity of 66 

Cabinets, construction of 138-141-168-204-354 

Cabinets, use of 138- 163- 168-204 

Cabinets for rheostats and auto-starters 84 

Cable, armored 315 



432 INDEX 



PACE 

Calculation of wires 40 

Canopy insulators 220 

Car wiring and equipment 275 

Car houses 283 

Care and attendance 73 

Carrying capacity table 4 T 3 

Ceiling fans 96-223 

Ceiling rosettes, construction of •. 356 

Ceiling rosettes, use of 232 

Central stations 47 

Choke coils 72 

Circuit breaker, construction of ZZ2> 

Circuit breaker, installation of 58-81-89-98-136-151-166 

Circuit breaker, how high may be set 166 

Circuit, open 9 

Circuit, closed 9 

Circuit, divided 16 

Circular mil 40 

Cleats 121-322 

Compensator coils 236 

Compensator sets, fusing of 58 

Concealed wiring 129-172-176-180-191 

Concentric wire 314 

Condensers 371 

Conductors 10 

Conductors. (See Wires.) 

Conduits, installation of 201 

Conduits, metal, construction of 315 

Conduits, wire for 313 

Conduit work 188-201 

Conduit work, outside 101 

Constant current system 32-141 

Constant potential system 33-151 

Converters. (See Transformers.) 

Convertible wiring systems 155-161 

Cooper-Hewitt lamp 235 

Coulomb 13 

Cranes, electric 287 

Crossing of constant potential pole lines over 5,000 volts. . 107 

Current 7~ l 3 

Current for motors _ 80-163-165-429 

Cutout cabinets. (See Cabinets.) 



index 433 



PAGE 

Cutouts, construction of 336 

Cutouts, installation of 136-151-163 

Cutouts, must protect all wires of the circuit 136 

Damp places 134-139-182-22S 

Decorative lighting system 237 

Distance between conductors, inside 144-180-191-292 

Distance between conductors, outside 100 

Divided circuits 16 

Dressing rooms, theaters 253 

Drip loops at service entrance 103-153 

Dynamo rooms 47 

Economy coils 236 

Electric bells 19 

Electric gas lighting 385 

Electric heaters 173 

Electrolytic corrosion of underground metal work 106 

Electrolysis 106-130 

Electro-magnetic devices for switches 148 

Electromotive force 11 

Electro plating 10 

Elevator cable 311 

Elevator shafts, wires in 135 

Equalizers 67-^66 

Exciters, fusing of 51 

Extra-high potential systems 295 

Fan motors hung from ceiling 96-223 

Feeders, railway 283 

Festoons 261 

Fished wires I75-IQ3 

Fittings and materials 296 

Fixtures 219-365 

Fixtures, canopies 219 

Fixture wire 312 

Fixture wiring 197 

Flexible cord, construction of 307 

Flexible cord, construction of, heater 310 

Flexible cord, construction of, pendants 308 

Flexible cord, construction of, portables 309 

Flexible cord, use of 230 



434 INDEX 



PAGE 

Flexible tubing, construction of 332 

Flexible tubing, where permitted 196 

Footlights, theater 243 

Foreign currents, protection against 380 

Formula for soldering fluid 124 

Fuses, construction of 337 

Fuses, installation of 151-165-404 

Fuses, protection for generators 51 

Gas lighting, electric 385 

Generators 47 

Ground clamps 211 

Ground connections 119 

Ground connections for transformers 115 

Ground detectors _ 61-74 

Ground plates, construction of 1 19 

Ground return wires, trolley system 106 

Ground wire for lightning arrestors 74-380 

Grounded trolley circuits 105 

Grounding interior conduits 208 

Grounding low potential circuits 118 

Grounding of dynamo and motor frames 47-78 

Grounding sheaths of cable 104 

Grounds, testing for 74 

Guards, irons or wires, use of 106-108 

Guard strips, inside work, where required 145-177 

Hanger boards, construction of 363 

Hanger boards^ when not used 146 

Heaters, electric 173 

High, constant potential system 292 

Incandescent lamps as resistance 69-234 

Incandescent lamps in series circuits 148-294 

Incandescent lamps where inflammable gases exist 227 

Induced currents 26 

Induction coil 25 

Inside work 121 

Insulated platforms at high potential machines 47-78 

Insulating joints, construction of 365 

Insulating joints, where required 219 

Insulation of fixture canopies, when required 219 



index 435 

PAGE 

Insulation of trolley wires 105 

Insulation resistance 74-385 

Insulators 10-122 

Insulators, spacing, inside work 144- 180- 19 1-292 

Interior conduits. (See Conduits.) 

Joints in conductors 102-124-184 

Joints, insulating. (See Insulating joints.) 

Junction boxes, installation of 199-203 

Knob and tube work 191 

Knobs, construction of 324 

Knobs, use of 121 

Lamps, arc. (See Arc lamps.) 

Lamps, incandescent, rating of 429 

Lightning arresters, construction of 372 

Lightning arrestors, installation of 71 

Lights from trolley circuits 287 

Loop system 193 

Loss in voltage 36 

Low potential systems 175 

Lugs for terminal connections, when required 

124-328-338-340-367 

Magnets 9 

Marine work 387 

Mechanical injury, protection against 145-177 

Mercury vapor lamps 234 

Meter connections 409 

Metering panels 349 

Mil, definition of 40 

Motors 78 

Motors, enclosure for 94 

Moulding, construction of 319 

Moulding work 185-217 

Moving picture machines 238-263 

Multiple-series systems 94- 

Neutral wire 33-152-402 

Ohm 12 



436 INDEX 



PAGE 

Ohm's law 13 

Oily waste 74 

Open wiring 179 

Outlet and switch boxes, construction of 318 

Outlet boxes or plates, conduit, when required 198-206 

Outline wiring 273 

Outside work 100 

Panel boards, construction of 348 

Pockets, stage 250 

Pole lines 101-104 

Pole lines, constant potential over 5,000 volts 107 

Pole lines, high pressure, near buildings 112 

Portable conductors 309 

Portable lamps, installation of 309 

Power 14 

Power from trolley circuits 287 

Power and transformer stations 47 

Protection for gas outlet pipes 219 

Protective devices on signal circuits, construction of.... 382 
Protective devices on signal circuits, installation of 380 

Railway power plants 98 

Railway wires. (See Trolley wires.) 

Reactive coils 371 

Receptacles. (See Sockets.) 

Reinforcing wires 159-421 

Resistance 12-17-41 

Resistance boxes. (See Rheostats.) 

Resistance for arc lamps, low potential 234 

Resuscitation 396 

Rheostats; construction of 366 

Rheostats, installation of 67-96-256-264 

Roof Wiring 101 

Rosettes, construction of 356 

Rosettes, use of 232 

Running boards, construction of 177 

Sag in outside wires 101 

Series arc system 32-141 

Series incandescent lamps 148-294 

Series-multiple system 35~94 



index 437 



PAGE 

Service blocks and wires ioo 

Service switches 141-152-167 

Service wires, underground . 136 

Signalling system 380 

Signs, electric . 372 

Sockets, construction of 358 

Sockets, installation of 227 

Soldering fluid, formula 124 

Soldering stranded wires 124 

Spark arresters, construction of 364 

Spark arresters, when required 146-234 

Speed controller 88 

Square mil 40 

Stage 'wiring 241 

Starting boxes 67-84 

Static electricity, overcoming 50 

Station and dynamo rooms 47 

Storage battery rooms 98 

Strip lights 258 

Stage cable, construction of 310 

Switchboards 63 

Switchboards, theater 241 

Switch boxes, conduit, construction of 318 

Switches, construction of, knife 326 

Switches, construction of, snap 330 

Switches, electro-magnetic 148 

Switches, flush, installation of 171 

Switches, installation of 136-141-167 

Switches, when may be single-pole 81-169- 173 

Switches, time 140 

Systems, alternating current 35 

Systems, constant current 32-141 

Systems, constant potential, general rules 151 

Systems, extra-high constant potential 295 

Systems, high constant potential 292 

Systems, low constant potential 175 

Systems, multiple-series 94 

Systems, of wiring 32-155 

Systems, series-multiple 94 

Systems, signalling 380 

Tables 413 to 430 



438 INDEX 



PAGE 

Tablet boards 348 

Telegraph, telephones and other signal circuits : 380 

Telephones 23 

Testing ' 74-220-400 

Theater wiring 238 

Three-wire generators, fusing of 51 

Three-wire systems 151-164-180-401 

Transformers, grounding of secondary 115 

Transformers, installation of, inside 99-1 13-237-293-371 

Transformers, installation of, outside 117 

Transformer stations 47 

Transmission, electric 36 

Transmission lines, constant potential over 5,000 volts . . 107 

Tree system of wiring 156 

Tricks of the trade *. 408 

Trolley wires 105 

Tubes, insulating 1 16-321 

Underground conductors 135 

Vacuum tube systems 235 

Volt 11 

Voltmeter, switchboard, circuit for 61 

Waterproof construction 182 

Waterproof pendants 229 

Watt 15 

Wire, concentric 314 

Wire, conduit 313 

Wire, construction, general rules 296 

Wire netting required on arc lamps 146-234 

Wire, rubber-covered 296 

Wire, slow burning T 179-306 

Wire, slow burning weather proof 179-305 

Wire, weatherproof 306 

Wireless telegraph 384 

Wires, calculation of 40 

Wires, car work 235 

Wires, carrying capacity table 413 

Wires, central station 60 

Wires, conduit work 188-313 

Wires, constant current system 141 



index 439 

Wires, in parallel 159-421 

Wires, in stations and dynamo rooms 60 

Wires, number in conduit 407 

Wires, extra high potential 295 

Wires, fished 175-193 

Wires, fixture work 312 

Wires, low potential, general rules 175 

Wires, high potential 292 

Wires, inside, constant current 141 

Wires, inside, general rules 121 

Wires, moulding work 185 

Wires, open work, damp places 182 

Wires, open work, dry places 180 

Wires, outside, overhead 100 

Wires, service 100-103 

Wires, signal 380 

Wires, trolley 105 

Wires, underground 135 

Wiring, systems 32-156 

Wiring tables 414 



FREDERICK J. DRAKE & CO.'S 

PRACTICAL MECHANICAL BOOKS 

FOR 

HOME STUDY 

Price. 
Titles. Cloth. Lea. 

Air Brake Practice, Modern — Dukesmith. 

Illustrated 1.50 ... 

Air Brake, Complete Examinations, West- 

inghouse and New York 2.00 

Air Brake, Westinghouse System 2.00 

Air Brake, New York System 2.00 

American Homes, Low Cost — Hodgson. Il- 
lustrated 1.00 

Architectural Drawing, Self - Taught — 

Hodgson. Illustrated 2.00 

Architecture, Easy Steps to — Hodgson. Il- 
lustrated 1.50 

Architecture, Five Orders — Hodgson. Il- 
lustrated 1.00 

Armature and Magnet Winding — Horst- 

mann & Tousley 1.50 

Artist, The Amateur — Delamotte 1.00 

Automobile Hand Book — Brookes. Illus- 
trated 2.00 

Automobile, The Mechanician's Catechism 

— Swingle 1.25 

Blacksmithing, Modern — Holmstrom. Il- 
lustrated 1.00 

Boat Building, for Amateurs — Neison. Il- 
lustrated 1.00 

Bricklayers' and Masons' Assistant, The 

20th Century — Hodgson. Illustrated.. 1.50 

Bricklaying, Practical, Self - Taught — 

Hodgson. Illustrated 1.00 

Bungalows and Low Priced Cottages — 

Hodgson 1.00 

Calculation of Horse Power Made Easy — 

Brookes. Illustrated 75 

Carpentry, Modern. Vol. I — Hodgson. Il- 
lustrated 1.00 

Carpentry, Modern. Vol. II — Hodgson. 

Illustrated 1.00 

Chemistry, Elementary, Self - Taught — 

Roscoe. Illustrated 1.00 

Concretes, Cements, Plasters, etc. — Hodg- 
son. Illustrated 1.50 

Correct Measurements, Builders' and Con- 
tractors' Guide to — Hodgson 1.50 

Catechism, Swingle's Steam, Gas and 

Electrical Engineering 1.50 

Cabinet Maker, The Practical, and Fur- 
niture Designer — Hodgson. Illustrated 2.00 

Dynamo Tending for Engineers — Horst- 

mann & Tousley. Illustrated 1.50 

Dynamo — Electric Machines — Swingle. Il- 
lustrated 1.50 

Electric Railway Troubles and How To 

Find Them — Lowe 1.50 

Electric Power Stations — Swingle 2.50 

Electrical Construction, Modern. Illus- 
trated 1.50 

Electrical Dictionary, Handy, Weber 25 .50 

Electrical Wiring and Construction Ta- 
bles — Horstmann & Tousley 1.60 

Electricity, Easy Experiments in — Dick' 

inson. Illustrated *.<** ••• 



Price. 

Titles. Cloth. Lea. 

Electricity Made Simple — Hasklns. Illus- 
trated 1.00 ... 

Electric Railroading — Aylmer-Small. Il- 
lustrated 3.50 

Electro - Plating Hand Book — Weston. 

Illustrated 1.00 1.50 

Elementary Electricity, Up To Date — 

Aylmer-Small 1.25 ... 

Estimator, Modern, for Builders and 

Architects — Hodgson 1.50 ... 

Examination Questions and Answers for 
Locomotive Firemen — Wallace. Illus- 
trated 1.50 

Examination Questions and Answers for 
Marine and Stationary Engineers — 
Swingle. Illustrated 1.50 

Elevators, Hydraulic and Electric — Swin- 
gle. Illustrated 1.00 . . . 

Electrician's Operating and Testing 
Manual — Horstmann & Tousley. Illus- 
trated . .V 1.5© 

Farm Engines and How to Run Them — 

Stephenson. Illustrated 1.00 ... 

Furniture Making, Home- — Raeth. Illus- 
trated .'.' 60 ... 



Gas ' and Oil Engine Hand Book — 

Brookes. Illustrated 1.00 1.50 

Hand Book for Engineers and Electri- 
cians — Swingle. Illustrated. Pocket 
Book Style 3.00 

Hardwood Finishing, Up-to-date — Hodg- 
son. Illustrated 1.00 ... 

Horse Shoeing, Correct — Holmstrom. Il- 
lustrated 1.00 ... 

Hot Water Heating, Steam and Gas Fit- 
ting — Donaldson. Illustrated 1.50 ... 

Heating and Lighting Railway Passen- 
ger Cars — Prior 1.25 . . . 

Locomotive Breakdowns, with Questions 

and Answers — Wallace. Illustrated 1.50 

Locomotive Fireman's Boiler Instructor — 

Swingle 1.50 

Locomotive Engineering — Swingle. Illus- 
trated. Pocket Book Style 3.00 

Machine Shop Practice — Brookes. Illus- 
trated 2.00 ... 

Mechanical Drawing and Machine Design 

— Westinghouse. Illustrated 2.00 ... 

Motorman, How to Become a Successful. 

Aylmer-Small. Illustrated 1.50 

Motorman's Practical Air Brake Instruc- 
tor — Denehie 1.50 

Modern Electric Illumination, Theory 
and Practice — Horstmann & Tousley. 
Illustrated 2.00 

Millwright's Practical Hand Book — Swin- 
gle. Illustrated ^.00 ... 

Modern American Telephony In All Its 

Branches — Smith. Illustrated - ZW 



Price. 
Titles. Cloth. Lea. 
Operation of Trains and Station Work — 
Prior. Illustrated 1.5Q 

Painting, Cyclopedia of — Maire. Illus- 
trated 1.50 ... 

Pattern Making and Foundry Practice — 
Hand. Illustrated 1.50 

Picture Making for Pleasure and Profit — 

Baldwin. Illustrated 1.25 ... 

Plumbing, Practical, Up-to-Date — Clow. 

Illustrated 1.50 ... 

Railway Roadbed and Track, Construc- 
tion and Maintenance of — Prior. Illus- 
trated 2.00 

Railway Shop Up-to-Date — Haig. Illus- 
trated 2.00 . 

Sheet Metal Workers' Instructor — Rose. 

Illustrated 2.00 . 

Signist's Book of Modern Alphabets — Del- 

amotte 1.50 . 

Sign Painting, The Art of — Atkinson... 3.00 . 

Stair Building and Hand Railing — Hodg- 
son. Illustrated 1.00 . 

Steam Boilers — Swingle. Illustrated 1. 

Steel Square, A Key to — Woods 1.50 . 

Steel Square, Vol. I — Hodgson. Illus- 
trated 1.00 . 

Steel Square, Vol. II — Hodgson. Illus- 
trated 1.00 . 

Steel Square, A B C — Hodgson 50 . 

Steel Construction, Practical — Hodgson. 

Illustrated ^ .50 . 

Storage Batteries — Niblett 50 . 

Sho' Cards, A Show At — Atkinson and 

Atkinson 3.00 . 

Stonemasonry, Practical, Self-Taught — 

Hodgson. Illustrated 1.00 • 

Telegraphy Salf-Taught — Edison. Illus- 
trated 1.00 . 

Telephone Hand-Book— Illus- 
trated 1.00 . 

Timber Framing, Light and Heavy — 

Hodgson 2.00 . 

Toolsmith and Steel Worker — Holford. 

Illustrated 1.50 . 

Turbine, The Steam — Swingle. Illustrated 1.00 . 

Walschaert Valve Gear Breakdowns and 
How to Adjust Them — Swingle. Illus- 
trated 1.00 . 

Wiring Diagrams, Modern — Horstmann 

& Tousley. Illustrated 1.50 

Wireless Telegraphy and Telephony — 

V. H. Laughter 1.00 

Wood Carving, Practical — Hodgson. Illus- 
trated 1.50 

THE RED BOOK SERIES OF TRADE SCHOOL 

MANUALS 

By F. Maire 

~^ mo., Cloth, Illustrated. Price, each, $0.60 

Exterior Painting, Wood, Iron and Brick, 
interior Painting, Water and Oil Colors. 
Jolors, What They Are and What to Expect 

,*ora Them. 

Graining and Marbling. 
Carriage Painting. 
The Wood Finisher. 






illlllh 

021 225 290 6 








